LAUNCH ACTIVITY 3 - Mr. Gauthier | Course...

98 MHR • Unit 2 Chemical Reactions

Underwater documentary films offer a peek into the amazing diversity of ocean life. Divers use specially designed movie cameras and tanks that let them breathe

underwater. But bubbles from regular scuba gear can scare wildlife and ruin a shot. That’s where rebreathers come in. A rebreather is a specialized recycling apparatus that adds oxygen to the air a diver breathes out and removes carbon dioxide from it. The exhaled carbon dioxide interacts in a water solution with a compound called calcium hydroxide in the rebreather. A solid substance called calcium carbonate is produced during this interaction. Removing carbon dioxide (followed by adding oxygen) allows exhaled air to be breathed again and again. No gas bubbles are released to the surroundings.

The change that occurs when carbon dioxide interacts with calcium hydroxide is one example of a chemical reaction. In this chapter, you will learn how to use the names and chemical formulas of different compounds to describe what happens to them, and to their properties, during chemical reactions.

NS Science 10 CH3.indd 98 12/3/11 3:26:40 PM

What You Will Learn

In this chapter, you will• describe the differences between ionic and

molecular compounds• name compounds and write their formulas• write chemical equations

LAUNCH ACTIVITY 3

A Carbon Dioxide Generator

In your body, cellular respiration consumes oxygen and generates carbon dioxide. But other chemical changes can also generate carbon dioxide.

Safety Precautions

• Dispose of materials as your teacher directs.

Materials• 250 mL Erlenmeyer flask with side arm• stopper• tubing• 150 mL beaker• scoopula• 25 mL graduated cylinder• baking soda• citric acid• limewater

What to Do 1. Set up the apparatus as shown. Add about 100 mL

limewater to the beaker.

2. Place half a scoop of baking soda in the flask. Add half a scoop of citric acid. Swirl the solids together and record your observations.

3. Add 20 mL of water to the flask and quickly place the stopper on the flask. Swirl the flask.

4. Observe what is happening both in the flask and the beaker. Record your observations.

What Did You Find Out? 1. Did a reaction occur in the flask? In the beaker? How

do you know?

2. In the test for carbon dioxide, the compound calcium hydroxide in the limewater reacts with carbon dioxide to form the compound calcium carbonate and water. How did the appearance of the liquid in the beaker change over time? What does this mean in terms of the amount of calcium carbonate produced?

3. Why do you think water was required for the reaction to proceed? Would a reaction have occurred if either citric acid or baking soda were left out?

4. How does this activity relate to what happens in a rebreather, described on the facing page?

Chapter 3 Chemical Names, Formulas, and Equations • MHR 99

Why It Is Important

Chemically literate people can make informed decisions about what products to buy and use and to help reduce human impact on the environment. A key part of chemical literacy is being able to interpret chemical names and formulas, as well as understand the chemical equations that represent those reactions.


Many of the chemical compounds in products that people use at home, school, and work have properties that make them both beneficial and potentially dangerous. For instance, compounds that include the element chlorine are included in many household cleaners because of their strong disinfectant properties. Chlorine kills bacteria and many other organisms because it is toxic (poisonous) to them. Its toxicity is what makes chlorine useful. However, its toxicity also means that people must use chlorine with great care.

Chlorine compounds are also used on a large scale to disinfect drinking water and swimming pool water, as shown in Figure 3.1. Although chlorine compounds are widely used, they must be produced, used, and disposed of carefully because of the hazardous nature of their properties. Many other compounds contained in cleaning products are also potentially dangerous, even though they are also useful for cleaning. That’s why many products sold for use in the home have hazard symbols and safety warnings on their packaging, as shown in the image on the next page.

Ionic and Molecular Compounds

Key Termsmolecular compoundmoleculeionionic compound

3.1

What Do You Think?• What are some examples of chemical compounds at home, and what are their

properties or uses?

• What kinds of things do people at home and in the workplace need to know

about the properties of substances to use them safely?

• What is the value of using the formula H2O to represent water or the formula

NaCl to represent table salt?

Figure 3.1 To keep the water in swimming pools free of harmful bacteria and other microbes, compounds containing chlorine are often added to the water to disinfect it.Infer Since chlorine is toxic to all organisms, including humans, what factors do you think are taken into account in order to add chlorine to swimming pools so they are safe for people?



Can You Judge a Product by Its Label?

3-1A Find Out ACTIVITY

Products used in the home have properties that make them useful for jobs such as cleaning clothes or shining glass. But these properties can also make them dangerous. Many home products that are potentially dangerous have safety warnings on their labels. Hazardous Household Product Symbols (HHPS) are designed to be easy to understand. The shapes that outline the pictures are designed to look like road signs.


The PICTURE tells you theTYPE of danger

READ THE LABELS EVERY TIMEAND STAY SAFE

There are two frames used around the symbols:

symbol

signal word

EXPLOSIVE The container can explode if heated or punctured. Flying pieces of metal or plastic from the container can cause serious injury, especially to eyes.

CAUTION means temporary injury may be frequent. Death may occur with extreme exposure.

DANGER means may cause temporary or permanent injury or death.

EXTREME DANGER meansexposure to very low quantities may cause death or temporary or permanent injury.

CORROSIVE The product can burn your skin or eyes. If swallowed, it will damage your throat and stomach.

FLAMMABLE The product or its fumes will catch fire easily if it is near heat, flames or sparks. Rags used with this product may begin to burn on their own.

POISON If you swallow, lick, or in some cases, breathe in the chemical, you could become very sick or die.

This frame means that the contents inside thecontainer are dangerous.

This frame means that the container is dangerous.

The back or side label of regulated containers will always have some type of bordered area. Inside the border. you will find safety instructions, the words FIRST AID TREATMENT along with instructions in case of injury and a list of harmful substances in the product.

KEEP OUT OF REACH OF CHILDREN

Avoid contact with eyes. Avoid inhalation.FIRST AID TREATMENTThis product contains ammonia.If splashed in eyes or on skin, flush thoroughly with water.If swallowed, drink large amounts of water. DO NOT INDUCEVOMITING. CALL PHYSICIAN OR POISON CONTROL CENTRE IMMEDIATELY.

What to Do 1. Work in small groups. Your teacher will provide your

group with an empty container for a common product used in the home or a label from a common product. Examine the label carefully.

2. What is the intended use of the product?

3. What substance or substances are found in the product?

4. What, if any, hazard-related information is included on the product labelling?

5. What, if any, safety-related instructions are provided?

6. Your teacher will provide MSDS for some of the substances in the product. What information is provided on an MSDS?

What Did You Find Out? 1. As a class, share some of the names of the substances

listed on the label.

2. Which substances are familiar to you? Which substances are unfamiliar?

3. Based on the names of the substances, what similarities and differences do you notice between ingredients in the products?

4. Do you notice significant differences between products that are labelled “green” and those that are not?

5. What do you think happens to the substances in these products once they are used in your home?

6. Should people stop using products that contain potentially dangerous compounds? Defend your answer.

7. How do the HHPS symbols compare with the WHMIS symbols? Refer to the front of your textbook to remind yourself of the WHMIS symbols.

8. Choose one compound from the class list. Conduct research to find out about its properties and any issues related to its production, use, or disposal. Briefly report your findings to the class.



Chemical CompoundsOne method for adding chlorine to the water in a pool involves breaking down sodium chloride, also known as table salt. (A certain company that uses this method brags that they use only the finest Nova Scotia salt!) Water and sodium chloride are both examples of chemical compounds. Some other familiar examples are shown in Figure 3.2.

In chemical terms, compounds are made of elements that are chemically combined in specific proportions. Take a look at the periodic table at the back of your book. There are 92 naturally occurring chemical elements, most of which can combine with one or more other elements to form compounds. Imagine how many combinations are possible!

Two Categories for Compounds

As you can see in Figure 3.2, even commonplace compounds have a wide variety of properties. One way that chemists make sense of compounds and their properties is to classify them. And two categories that chemists use for compounds are molecular compounds and ionic compounds. Chemicals in these two categories share similar properties, which can be explained by their structure at the atomic level.

Molecular CompoundsWater, sugar, and carbon dioxide may seem like very different substances. Water is a clear liquid at room temperature, while sugar is a white solid and carbon dioxide is a clear gas. But they have one important thing in common that makes them all molecular compounds. All three substances are made of atoms of non-metal elements joined together as molecules.

Figure 3.2 Chemical compounds include objects we use, food we eat, and the air we breathe.Analyze What patterns in the properties of these ionic and molecular compounds do you notice?molecular compound a

compound formed of atoms of two or more elements that share electrons

air – a mixture of elements and molecular compounds that include carbon dioxide and water

butter – a mixture of molecular compounds made of carbon,

hydrogen, and oxygen

wood – mainly cellulose, a molecular compound

made of carbon, hydrogen, and oxygen

melamine plastic – molecular compounds

made of carbon, nitrogen, and hydrogen baking soda –

sodium hydrogen carbonate, an ionic compound made of sodium, hydrogen, carbon, and oxygen

table salt – an ionic compound made of sodium and chlorine

sugar – a molecular compound made of carbon,

hydrogen, and oxygen

eggshells – calcium carbonate, an ionic compound made of calcium, carbon, and oxygen

molecule particle formed by two or more atoms joined by covalent bonds

Did You Know?

How many compounds are currently known to science? It is a difficult question to answer because there are so many. Estimates differ, but all agree that there are many millions. Scientists also agree that many millions more are possible– over 100 000 new compounds are being made each year.



hydrogen atoms

covalentbonds

oxygenatom

Figure 3.3 Water is composed of molecules. Water molecules consist of two hydrogen atoms bonded to one oxygen atom.

Molecules

A molecule is the smallest independent unit of a molecular compound, and it consists of atoms of different elements bonded together. For example, water consists of two hydrogen atoms and one oxygen atom bonded together as shown in Figure 3.3. The bonds between the atoms are called covalent bonds and they are very strong. Covalent bonds form when atoms share electrons. Think of a covalent bond as a tug-of-war game. Two teams are joined by the rope but prevented from coming together by the opposite forces they are exerting.

Explaining Some Properties of Molecular Compounds

Molecular compounds have widely varying properties. The plastic casing of a ball-point pen, the components of gasoline, the strongly scented compounds in a banana, and the carbon dioxide that we exhale with every breath are all molecular compounds. But there are some properties that many molecular compounds share, due to the way molecular compounds are structured at the molecular level.

Although the bonds that hold atoms together in molecules are very strong, the bonds that attract one molecule to another in a molecular compound are relatively weak, as modelled in Figure 3.4. When you melt or vaporize a molecular compound, you need to supply enough energy to overcome the attraction between the molecules. Because this attraction is weak, most molecular compounds boil and melt at relatively low temperatures. This property also explains the relative softness of molecular compounds.

In addition, because molecular compounds do not have free electrons or ions, they are relatively poor conductors of electricity and heat. Figure 3.5 shows an application of this property.

relatively weak bonds

strong covalent bonds

Figure 3.4 The bonds that hold atoms together in molecules—covalent bonds—are very strong. Compared to these covalent bonds, the bonds that hold one molecule to another are very weak.

Figure 3.5 Molecular compounds are poor conductors of electric current. This makes them useful as insulating covers for computer cables. Apply Why is it important that covers for electrical wires not conduct electric current?



Ionic CompoundsSome compounds are not made of molecules. Instead, they are made of ions. An ion is an atom or group of atoms with a positive or negative charge. Compounds made of ions are called ionic compounds. Ionic compounds consist of negatively charged ions and positively charged ions held together with ionic bonds, which is the name for the attraction between oppositely charged ions. Ionic bonds are very strong.

Ionic compounds containing two elements form when atoms of one element each lose one or more electrons to atoms of the second element. For example, table salt, sodium chloride, forms when sodium atoms each transfer one electron to chlorine atoms. Each sodium atom becomes positively charged: a positive ion. Each chlorine atom becomes negatively charged: a negative ion. This is what happens when sodium metal reacts with chlorine gas to form sodium chloride, as shown in Figure 3.6.

ion an atom or group of atoms with a positive or negative charge

Word Connect

The term “ion” comes from a Greek word that means “going.” Physicist Michael Faraday (1791–1867) first used the term for substances that conduct electric current in solution—in other words, substances that allow the current to “go.”

Figure 3.6 A sodium atom loses one electron to a chlorine atom, forming a sodium ion, Na, and a chloride ion, Cl. Joined by strong ionic bonds, they form the compound sodium chloride.

Check Your Understanding 1. What is a molecule? Provide a sketch as part of your answer. 2. Give two examples of molecular compounds. 3. “The bonds in molecular compounds are very strong.” Do you

agree or disagree with this statement? Explain your answer. 4. Why do molecular compounds tend to boil and melt at relatively

low temperatures? 5. What is an ion? Give two examples of ions. 6. Give two examples of ionic compounds.

e–

Na+ Cl–ClNa

ionic compound a compound composed of oppositely charged ions held together with ionic bonds

→

sodium chlorine sodium chloride



The Structure of Ionic Compounds

Unlike molecular compounds, ionic compounds do not consist of discrete units (molecules). Instead, they form large structures with regular and repeating patterns called lattices. The cubic structure of sodium chloride is an example of a lattice. Notice the cubic shape of the sodium chloride crystals in the magnified image in Figure 3.7. A model of the lattice arrangement of ions of sodium chloride is shown in Figure 3.8.

Explaining Some Properties of Ionic Compounds

To melt or boil an ionic compound requires breaking the strong ionic bonds holding the ions together in a lattice structure. Because the bonds are so strong, a great deal of energy is required to do this. As a result, ionic compounds tend to melt and boil at very, very high temperatures. For example, the melting point of sodium chloride is 801°C.

Ionic compounds do not conduct electricity in the solid state. Even though they are made of ions, those ions are held rigidly in place. Charged particles that can move are required to conduct an electric current. Ionic compounds dissolved in water or melted ionic compounds do, however, conduct electricity. In those forms, the ions in ionic compounds are free to move around.

Patterns in Ion Formation3-1B Think About It

What to Do 1. Take a look at the periodic table. Notice that many of

the element cells have one or more charges listed in the upper righthand corner. According to the periodic table’s key, what are these charges?

2. Look at the groups of the periodic table. What patterns in ion charges do you notice?

What Did You Find Out? 1. Refer to the periodic table. What ions are formed by

elements from Groups 1, 2, 16, 17, and 18? Make generalizations for each.

2. What are some elements you would not expect to find in ionic compounds? Explain your answer.

Figure 3.8 A crystal of sodium chloride is structured so that six chloride ions surround every sodium ion, and six sodium ions surround every chloride ion. They are all joined by strong ionic bonds. Explain Sodium chloride is formed of charged particles, but the compound overall has no charge. Why?

Investigation 3-1C: Properties of Ionic and Molecular Compounds

Suggested Activity

Figure 3.7 This scanning electron microscope image shows smaller sodium chloride crystals on a large crystal. The image has a magnification of 558x. Each crystal contains millions and millions of sodium ions and chloride ions.



Safety Precautions

• Wear safety eyewear and a lab apron.

• Test for odour cautiously. Do not smell any chemicals in the laboratory directly. Follow the instructions given.

• Treat the hot plate carefully. Do not leave it turned on for more than 2 min. Allow it to cool for 15 min before moving it.

• To unplug the hot plate, do not pull on the cord. Pull on the plug.

Materials• 6 test tubes with stoppers

• 6 samples of compounds

• glass plate or watch glass

• scoop

• plastic water bottle

• hot plate

• aluminum foil

• distilled water

• conductivity tester

• tongs

Although each compound has unique properties, there are some similarities in these properties that can help you to tell what kind of compound it is. In this investigation, test six different compounds to determine whether they are ionic or molecular.

QuestionHow can you use properties to classify compounds as ionic or molecular?

Procedure1. Label six test tubes A to F. Place samples of six different compounds in the test

tubes. Use enough of each compound to fill the rounded bottom of the test tube.

2. Prepare a table like the one shown. It should take up one full page so you have enough space for all your observations. Give your table a title.

3. Perform the following tests on each compound. At each test step, analyze all the compounds before moving on to the next test. If a substance responds like a molecular compound, record a score of one (1). If a substance responds like an ionic compound, record a score of zero (0). Also record short, descriptive observations for each test in your table.

Crush Test Place one or two grains of the compound on a glass plate or watch glass. Press on the compound with a scoop or another metal tool. Ionic compounds withstand considerable force and then crush suddenly into a gritty powder (score 0). Solid molecular compounds are often more flexible and crush like wax or plastic (score 1).

Hardness Test You must wear gloves for this test. Wash and dry your gloves after each substance. Rub some of each compound on a clear plastic water bottle. Ionic compounds are often hard enough to scratch the plastic (score 0). Molecular compounds are seldom hard enough to scratch the plastic (score 1).

Melting Test Spread a square of aluminum foil to cover the entire surface of the hot plate. Carefully place one small piece (no larger than half a grain of rice) of each substance on the aluminum. Place the samples as far apart as possible but avoid the edges of the hot plate. Plug the hot plate into the electric outlet. Turn on the hot plate. Ionic compounds do not melt except at very high temperatures (score 0). Many molecular compounds melt at relatively low temperatures (score 1). Turn off the hot plate after 2 min. When the hot plate has cooled, pull out the plug. Do not pull on the cord.

Properties of Ionic and Molecular Compounds

SkillCheck• Observing

• Recording

• Analyzing and Interpreting

• Communicating

3-1C

Substance A B C D E F

Crush

Hardness

Melting

Solubility

Conductivity

TOTAL score



Conduct an InVesTIgATIOn

Solubility Test Each test tube should still contain most of the original substance. Add 10 mL of distilled water to each of the test tubes. Stopper each test tube. Keeping your fingers on the stopper and test tube, gently shake or swirl the water and substance together. Many ionic compounds will dissolve in water, although there are exceptions (score 0). Many molecular solids are insoluble in water (score 1), although again there are exceptions.

Conductivity Test Use a conductivity tester to test the conductivity of the solution in each test tube. When ionic compounds dissolve, the resulting solution will conduct electricity (score 0). When molecular compounds dissolve, the resulting solution will usually not conduct electric current (score 1). Make sure that you clean the probes of the conductivity tester between readings.

4. Clean up your work area. Dispose of all the compounds as indicated by your teacher. Return each piece of equipment to its place.

Analyze1. Add up the scores for each compound. A low score, near 0, indicates that a

compound is ionic. A high score, near 6, indicates that the compound is molecular. What patterns do you see?

2. If a compound has a score of 2, 3, or 4, use your descriptive observations to help you decide whether it is ionic or molecular.

Conclude and Apply1. Summarize your classification of each substance including a rationale for each

decision.

2. What was the purpose of assigning a number to each test? Did the numbers have any scientific meaning?

3. If you could perform only two tests to identify ionic and molecular compounds, which two tests would you choose? Explain your thinking. If these tests are more important than the others for classifying, how could you reflect that in the scoring system if you were to perform the investigation again?

4. Your teacher will tell you the names and formulas of the compounds. What do the names and formulas tell you, if anything, about the compounds?

5. Examine the element symbols in the chemical formulas. What do you notice about the elements that are in the formulas for the ionic compounds compared to the elements that are in the formulas for the molecular compounds?



Testing, Testing…with Tox21In 2010, the explosion and fire on the drilling rig Deepwater Horizon sent oil gushing into the Gulf of Mexico, endangering wildlife and the environment. Officials had to act quickly. Part of the response was to use a certain group of chemicals to disperse the oil, allowing for easier clean-up. First, however, government scientists needed to test the chemicals to ensure they did not pose a threat to human health. And they needed to do it fast.

For this work, it helped to have a bright yellow robot as a lab assistant. A high-speed robotic arm conducted the tests for potential toxicity without having to expose humans or other living things to the chemicals. Using the robot was speedy and efficient. In just one day, the robot could run tests that would keep a human lab technologist busy for a year.

The Tox21 RobotThe robot is part of a screening system called Tox21. The system is an assessment tool that helps protect the health of humans and the environment by testing how chemicals react with laboratory preparations of living cells. Scientists want to understand how the chemicals found in various products, including food additives and prescription drugs, react with the chemicals already present in the human body and the environment.

In the past, toxicity tests were often done on animals. In the Tox21 system, however, a test chemical is added to a plate that has about 1500 small depressions or wells. Each well holds a different type of cell derived from human tissues. As the robot scans the cells to record any chemical reactions between the test chemical and the cells, scientists monitor the resulting data on computer screens. Any chemicals that disrupt normal cell function are cause for concern.

The Tox21 testing system is a significant new tool for the science of toxicology, which is the study of how chemicals can act as poisons when they react with other chemicals in living things and in the environment. The system represents a revolutionary shift in the science, which is moving from testing a few doses on animals, to the ability to test chemicals at a broad range of dosages using cells in the laboratory.

Eventually, the Tox21 system will be able to assess over 10 000 chemicals. Working day and night, 7 days a week, it will also help reduce the backlog of untested chemicals—a task that will save time and money, while vastly improving our understanding of chemical toxicity.

Questions

1. Describe the advantages of using the Tox21 system over the ways that toxicology studies have been done in the past.

2. Why is it important that different dosages of chemicals be tested on animal cells?



Checking Concepts1. Using an example, explain how a compound

can have properties that make it both useful and hazardous.

2. What does the acronym HHPS stand for, and what shapes are used to indicate the level of danger? Include the symbols that are used in the classification on HHPS labels.

3. Identify two categories that chemists use to classify compounds. Explain how a compound is classified into one of these two categories.

4. Describe the difference between an atom and an ion.

5. Identify which of the following are chemical compounds: an iron nail, ice cream, hand sanitizer, a plastic bottle, mercury in a thermometer, air, paper.

6. Make a table to compare ionic compounds and molecular compounds. Include columns for examples of each and descriptions of characteristic properties.

7. Compare and contrast the bonds in molecular compounds and ionic compounds.

8. Ionic compounds are made up of charged particles, ions, and yet the compounds themselves are electrically neutral. How is this possible?

9. An element on the periodic table has a 3 in the upper right hand corner of its element cell. What does this 3 mean?

Understanding Key Ideas10. Explain the term “lattice structure” as it

applies to an ionic compound such as sodium chloride.

11. Explain why calcium chloride does not conduct electric current as a solid but does conduct electric current in solution.

12. In a small coastal fishing village, the community works together to catch, clean, process, and ship their products to the rest of the world. If the population of the community were atoms, would the village be more like a molecular or an ionic compound? Explain your answer.

13. If a new element has been discovered that is found to behave chemically like sodium, is it more likely to form ionic or covalent bonds in compounds? Explain your answer.

14. Consider the following observations. • In most places, tap water conducts electric

current. • Purified water that contains no dissolved

substances conducts very little electric current, but it does conduct some.

• In the liquid state, a small percentage of water molecules form the ions H and OH.

Based on these observations, answer the following questions. Explain each answer.

(a) Would you expect a sample of water consisting only of water molecules to conduct electric current?

(b) What type of compound is likely contained in tap water?

(c) Why is it important to make sure your hands are dry when working with electrical equipment?

(d) Why does even water from which all other compounds have been removed conduct electric current to a small extent?

15. Candle wax is soft to the touch and requires only a small amount of heat to melt. Would these two observations lead to the conclusion that the candle wax is an ionic or a molecular compound? Explain your answer.

16. An element in Group 1 on the periodic table forms ionic compounds with elements in Group 17 in a 1:1 ratio. What ratio would you expect an element from Group 2 and elements from Group 16 to have when they form ionic compounds? Explain your answer.

17. Would you expect melted magnesium chloride to conduct electricity? Explain your answer.

Why is it important to understand the properties of different categories of compounds when planning and analyzing a chemical investigation?

Project Prep


Key Termsbinary ionic compound

Names and Formulas of Ionic and Molecular Compounds

3.2

What Do You Think?• Imagine that you have to create unique, distinctive names for a set of one

hundred or more objects such as seashells or computer emoticons. What criteria

(characterizing features) could you use?

• One example of a criterion for naming a compound is that the name should

indicate something about its composition. What other criteria do you think

scientists use to name ionic compounds and molecular compounds?

• What information does a chemical formula such as NaCl convey?


What’s in a Name?3-2A Think About It

Are there any patterns in the names of molecular and ionic compounds? Work with a partner to discover what information you can get from some chemical names. Note that each compound in this activity is composed of two elements only.

What to Do 1. Review the names of the molecular compounds listed

below. Note where each element in the compound is located on the periodic table. List at least two patterns that you can find in how the names are written. Write at least two questions that you have about the names of molecular compounds.

(a) dinitrogen trioxide

(b) nitrogen trichloride

(c) carbon disulfide

(d) tetraphosphorus decaoxide

(e) phosphorus pentabromide

2. Review the names of the ionic compounds listed below. Notice where each element in the compound is located on the periodic table. List at least two patterns that you can find in how these names are written. Write at least two questions that you have about the names of ionic compounds.

(a) sodium bromide

(b) magnesium sulfide

(c) iron(III) oxide

(d) lead(IV) nitride

(e) aluminum fluoride

(f) calcium chloride

What Did You Find Out? 1. What are two ways to distinguish ionic compounds

from molecular compounds based on the compounds' names?

2. What information is included in the name of a molecular compound that is not included in the name of an ionic compound?



Names of Binary Ionic CompoundsThe large bulging mass around the person’s neck in Figure 3.9 is called a goitre. Such a growth is caused by iodine deficiency. This problem is uncommon in developed countries because the ionic compound potassium iodide is added to our table salt.

Potassium iodide is an example of a binary ionic compound. In chemistry, “binary” means “composed of two elements.” Binary ionic compounds are composed of ions of one metal element and ions of one non-metal element joined by ionic bonds. The name of a binary ionic compound comes from the names of its elements as described below.• The first part of “potassium iodide” names the positive ion,

potassium, K. The positive ion is always a metal in a binary ionic compound. The positively charged metal ion is always named first. Its name is the same as the name of its element.

• The second part of “potassium iodide” names the negative ion, iodide, I, an ion of iodine. The negative ion in a binary ionic compound is always a non-metal. The name of the negative ion in a binary ionic compound always ends with the suffix “-ide.” (The negative ion of iodine is iodide.)

The names and symbols of common negative ions of non-metals are shown in Table 3.1. The ion charges are also found on the periodic table at the back of your textbook.

binary ionic compound a compound composed of ions of two different elements: a positively charged metal ion and a negatively charged non-metal ion

Figure 3.9 The goitre shown here results from a thyroid gland that enlarges as it attempts to absorb more iodine. Fish are an excellent natural source of iodine, so people who live near the sea and eat a lot of fish are not likely to suffer from goitres caused by iodine deficiency.

Table 3.1 Ions of Non-metals

Element Ion Symbol Group

fluorine fluoride F 17

chlorine chloride Cl 17

bromine bromide Br 17

iodine iodide I 17

oxygen oxide O2 16

sulfur sulfide S2 16

selenium selenide Se2 16

nitrogen nitride N3 15

phosphorus phosphide P3 15


The Structure and Formulas of Ionic Compounds

3-2B Think About It

As you know, ionic compounds consist of ions bonded together. For example, sodium chloride (table salt) is made of sodium ions and chloride ions. The diagram below represents part of a salt crystal. From the diagram, you can see how a crystal of salt is structured. How does the structure relate to the formula of sodium chloride?

What to Do 1. Examine the diagram carefully to see how the sodium

and chloride ions are arranged.

2. Count the total number of ions of each element that are represented in the model.

(a) How many sodium ions are represented?

(b) How many chloride ions are represented?

What Did You Find Out? 1. What is the ratio of sodium ions to chloride ions in

sodium chloride? In other words, how many sodium ions are there for every one chloride ion?

2. The chemical formula for sodium chloride is NaCl. Based on this model, should the formula be Na18Cl18? Explain why or why not.

3. What does the formula NaCl mean?

4. Given the chemical formula of the ionic compound beryllium fluoride, BeF2, what do you expect to be the ratio of beryllium ions to fluoride ions?

ClNa

subscripts

positive ion (Al3+) negative ion (O2–)

Al2O3

Figure 3.10 Anatomy of the formula of an ionic compound. Formulas for ionic compounds are always written with the positive ion first and the negative ion second. In binary ionic compounds, the positive ion is a metal and the negative ion is a non-metal.

1 K+ ion : 1 I– ion

KI

K+ I–

Figure 3.11 The subscripts in chemical formulas of ionic compounds tell you the ratio of the ions in the compound.

1 Mg2+ ion : 2 Cl– ions

MgCl2

Mg2+ Cl–

Cl–

2 Al3+ ions : 3 O2– ions

Al2O3

Al3+ O2–

Al3+ O2–

O2–

Interpreting the Chemical Formula of an Ionic CompoundThe chemical formula of a binary ionic compound contains element symbols to identify each ion. The positively charged metal ion comes first and the negatively charged non-metal ion comes second, as shown in Figure 3.10.

Some formulas have small numbers, called subscripts, written to the right of one or both symbols. The subscripts indicate the ratio of each type of ion in the compound. If no subscript is shown, you assume the number to be 1. For example, the formula Ag2O means Ag2O1. Examine Figure 3.11 to see some examples of chemical formulas of binary ionic compounds, and their meanings.




Check Your Understanding 7. Examine the periodic table and compare it with Table 3.1. What

do you notice about the locations of the elements listed in the table and the charges of the ions they form?

8. Which of the following ionic compounds are binary ionic compounds and which are not? Explain your answer.

(a) KCl (b) Al2O3 (c) NaNO3 (d) NH4Cl 9. Write the names of ionic compounds containing the following

elements. (a) rubidium and bromine (b) oxygen and magnesium (c) strontium and fluorine 10. Write the names of the following ionic compounds. (a) KBr (c) MgSe (e) Li3N (g) BeF2 (b) MgCl2 (d) Na2S (f) AlBr3 (h) RbBr

Writing Formulas of Ionic CompoundsAlthough an ionic compound is made up of ions, overall the compound is electrically neutral—it has no charge. So the positive charges on the metal ions must balance the negative charges on the non-metal ions. For example, in aluminum oxide, Al2O3, there are two aluminum ions, Al3, and three oxide ions, O2. What is the total charge?

When writing the formula of a binary ionic compound, you first need to determine the charges on the ions. Table 3.1 lists the ions of non-metals. For metals that form only one type of ion, all you need to do to figure out the ion charge is to look at the periodic table, as shown in Figure 3.12. (You can find the charges for non-metal ions on the periodic table, too.) Once you know the charges, you can figure out the formula.

Charge from Al3 Charge from O2

There are 2 aluminum ions in the formula, each with a charge of 3.

2 (3) 6

There are 3 oxide ions in the formula, each with a charge of 2.

3 (2) 6

Total charge: (6) (6) 0

118

(294)

Uuo*Ununoctium

Group 2 metals all form ions witha charge of 2+.

Notice that some metals can form more than one ion.

Group 1 metals all form ions with a charge of 1+.

Figure 3.12 The periodic table lists the charges of ions commonly formed by the various elements.



Sample Problem: Writing the Formulas of Ionic CompoundsProblemWhat are the chemical formulas of(a) calcium chloride? (b) aluminum sulfide?

Solution(a) calcium chloride

1. Identify each ion and its charge. calcium: Ca2 chloride: Cl

2. Determine the number of ions needed to balance positive charges with negative charges. In this case, two chloride ions are needed to balance the charge on calcium.

3. Use subscripts to write the formula. Remember to write the metal ion first. Do not include a subscript if the subscript would be “1.”

The formula for calcium chloride is CaCl2.

Solution(b) aluminum sulfide

1. Identify each ion and its charge. aluminum: Al3 sulfide: S2

2. Determine the number of ions needed to balance positive charges with negative charges. In this case, two aluminum ions are needed to balance the charges on three sulfide ions.

3. Use subscripts to write the formula. Remember to write the metal ion first. Do not include a subscript if the subscript would be “1.”

The formula of aluminum sulfide is Al2S3.

continued on next page

Charge from Ca2 Charge from Cl

A calcium ion has a charge of 2.

1 (2) 2

A chloride ion has a charge of 1. Therefore, two chloride ions are needed to balance the charge of one calcium ion.

2 (1) 2

Charge from Al3 Charge from S2

An aluminum ion has a charge of

3.

The lowest common multiple of 3 and 2 is 6. To get 6, multiply 3 by 2.

2 (3) 6

A sulfide ion has a charge of 2.

To get 6, multiply 2 by 3.

3 (2) 6



Sample Problem: Writing the Formulas of Ionic Compounds—continued

Check Your SolutionIn each case, the symbol for the metal is written first and the symbol for the non-metal comes second. The ratio of charges results in a neutral compound in both cases.For CaCl2: 1 (2) 2 (1) 0For Al2S3: 2 (3) 3 (2) 0

Practice Problems 1. Write the formulas of the ionic compounds containing the

following ions. (a) Na and Br (b) K and S2 (c) Zn2 and I

(d) Mg2 and N3

2. Write the formulas of the following ionic compounds. (a) sodium iodide (f) aluminum iodide (b) zinc oxide (g) aluminum phosphide (c) magnesium chloride (h) calcium oxide (d) potassium selenide (i) calcium sulfide (e) silver sulfide (j) rubidium bromide 3. Silver iodide has a crystal structure similar to ice and can cause

water to freeze. It has been used in rainmaking experiments, in which a substance is released into clouds to try to induce precipitation. A silver iodide generator is shown in Figure 3.13. What is the chemical formula of silver iodide?

Figure 3.13 This Cessna 210 single-engine airplane is equipped with a silver iodide generator. It is designed for cloud seeding experiments.



Multivalent MetalsAs you can see when you examine the periodic table, some metals form more than one type of ion. Such metals are called multivalent metals. For example, copper can form ions with a 1 or 2 charge, as shown in Figure 3.14. To distinguish between the ions, a Roman numeral is written after the name of the metal. For example, Cu is written as copper(I), pronounced “copper one.” Cu2 is written as copper(II), pronounced “copper two.” On the periodic table, the ion charges for a given element are listed with the most common charge at the top and the least common charge at the bottom.

Chemical Formulas and Names of Ionic Compounds Containing Multivalent Metals

To write the chemical formula of a multivalent metal, follow the same process as for the binary ionic compounds you have been naming so far. The only difference is that you cannot tell the charge on the metal ion by looking at the periodic table because there will be more than one choice. Instead, look at the Roman numeral in the name, which will tell you the charge.

The Roman numerals for charges 1 through 7 are given in Table 3.2. For example, the name chromium(III) chloride (shown in Figure 3.15) tells you that the chromium ion in the compound is Cr3. The chloride ion is Cl. For a neutral compound, there must be three chlorine ions for every one chromium ion, so the formula is CrCl3.

When naming a compound that contains a multivalent ion, you must include a Roman numeral to show which charge the ion has. You can determine the charge of the positive ion by determining the charge of the negative ion in the compound, as shown in the Sample Problem on the next page.

Figure 3.14 Although both of these compounds contain copper and oxygen, copper(II) oxide, CuO, is black and copper(I) oxide, Cu2O, is red. Infer What does the colour difference indicate about the two samples?

Figure 3.15 Like many compounds of chromium, chromium(III) chloride is vividly coloured. In fact, the name “chromium” comes from the Greek word for “colour.”

Table 3.2 Roman Numerals

Metal Ion Roman Charge Numeral

1 I

2 II

3 III

4 IV

5 V

6 VI

7 VII

Word Connect

As their name suggests, Roman numerals were first used by the ancient Romans. Their numeral system used letters from the Latin alphabet —I (1), V (5), X (10), L (50), C (100), D (500), and M (1000)—to express large and small numbers. For example, the year 2012 is MMXII in Roman numerals.



Check Your Understanding 11. What is the name of each of the following metal ions? (a) V4 (b) Ni3 (c) Au (d) Ti4

12. Write the formula for these compounds with a multivalent metal. (a) nickel(III) chloride (c) copper(I) oxide (b) lead(IV) sulfide (d) copper (II) oxide

Sample Problem: Naming an Ionic Compound with a Multivalent MetalProblemThe compound Fe2O3 is used as a source of iron in the steel industry. Figure 3.16 shows an example of Fe2O3 in nature. What is the name of Fe2O3?

Solution 1. Identify the ions. The ion of iron may be either Fe2 or Fe3. The ion of oxygen is O2. 2. Determine the ratio of ions in the compound. • According to the formula, the compound has 2 iron ions

for every 3 oxygen ions. 3. The negative charges and the positive charges must be equal

in magnitude. Determine which of the two possible iron ions achieves this balance.

• Since there are 3 oxygen ions, there is an overall negative charge of 6.

• Since there are 2 iron ions, they must have a charge of 3 to give an overall positive charge of 6.

4. Write the name of the compound using a Roman numeral to indicate the charge of the metal ion.

• The name of Fe2O3 is iron(III) oxide.

Check Your SolutionTwo Fe3 ions have a charge of 6. Three O2 ions have a charge of 6. The charges balance.

Figure 3.16 The famously red soil of Prince Edward Island gets its colour from compounds of iron, including Fe2O3(s).

Practice Problems 4. Write the names of the compounds with the following ions. (a) Co3 and O2 (c) Cu2 and Cl

(b) Mn4 and S2 (d) Cu and Cl

5. Write the names of the following compounds. Each contains an ion of a multivalent metal.

(a) FeO (c) SnS2 (e) Ni2S3 (g) PbF4 (b) Cu3N (d) Sn3N2 (f) NiS (h) TiS2



Ionic Compounds Containing Polyatomic IonsLimestone is an important industrial mineral that is mined in several locations around Nova Scotia. Limestone is made of an ionic compound called calcium carbonate, CaCO3, which is also the compound that shells such as those shown in Figure 3.17 are made of.

The carbonate ion, CO32, is composed of carbon and oxygen atoms.

An ion that, like carbonate, is composed of atoms of more than one element is a polyatomic ion. Compounds containing polyatomic ions are not binary compounds because they always contain at least three elements. But like binary compounds, compounds containing polyatomic ions are named by writing the name of the positive ion followed by the name of the negative ion.

Common Polyatomic Ions

There are a limited number of polyatomic ions that regularly occur in compounds. You can look up their names, formulas, and charges in a table such as Table 3.3. Notice that the only positively charged polyatomic ion listed is the ammonium ion, NH4

.

Table 3.3 Names, Formulas, and Charges of Some Common Polyatomic Ions

1 Charge 1 Charge 2 Charge 3 Charge

ammonium,

NH4

acetate, C2H3O2

chlorate, ClO3

chlorite, ClO2

hydrogen carbonate, HCO3

hydroxide, OH

nitrate, NO3

nitrite, NO2

permanganate, MnO4

carbonate, CO32

chromate, CrO42

dichromate, Cr2O72

peroxide, O22

sulfate, SO42

sulfite, SO32

phosphate, PO43

phosphite, PO33

Figure 3.17 Shellfish use calcium carbonate to make their shells.Research From what sources do shellfish get calcium carbonate?

Sample Problem: Writing Chemical Formulas of a Compound with a Polyatomic IonProblemCalcium nitrate is a key component of nitrogen-containing fertilizers. Important as a way to increase the yield of farms, such fertilizers can also cause problems when an excess of nitrogen enters waterways. What is the formula of calcium nitrate?

Solution 1. Identify each ion and its charge. (Use Table 3.3 or another

table of polyatomic ions to identify the polyatomic ion.) calcium: Ca2 nitrate: NO3

continued on next page



Sample Problem: Writing Chemical Formulas of a Compound with a Polyatomic Ion—continued 2. Determine the number of ions needed to balance positive

charges with negative charges. In this case, two nitrate ions are needed to balance the charge on calcium.

3. Use subscripts to write the formula. If the polyatomic ion is going to take a subscript, use brackets to enclose the polyatomic ion before adding the subscript as shown. This shows that the nitrate ion is a unit, and that there are 2 of them for each calcium ion.

The formula of calcium nitrate is Ca(NO3)2.

Check Your Solution

The symbol for the metal is written first and the symbol for the polyatomic ion comes second. The ratio of charges results in a neutral compound.

1 (2) 2 (1) 0

Charge from Ca2 Charge from NO3

A calcium ion has a charge of 2.

1 (2) 2

A nitrate ion has a charge of 1. Therefore, 2 nitrate ions are needed to balance the charge of one calcium ion.

2 (1) 2

Practice Problems 6. Write the formula of each of the following compounds. (a) barium nitrate (e) sodium dichromate (b) potassium carbonate (f) iron(II) chromate (c) nickel(II) sulfate (g) lead(IV) acetate (d) magnesium phosphate (h) ammonium sulfate 7. There is an error in each of the formulas of the following ionic

compounds. Explain the error and correct each formula. (a) sodium phosphate, Na3P (b) magnesium nitrate, MgNO32 (c) potassium sulfite, KSO3 (d) sodium hydroxide, Na(OH) 8. The crystals shown in Figure 3.18 are the largest so far

discovered on Earth. Formed naturally in very hot and humid conditions, the crystals are made of the compound calcium sulfate. What is the formula of calcium sulfate?

Figure 3.18 These enormous natural calcium sulfate crystals are located in a 290-m-deep cave in Mexico called Cueva de los Cristales. The conditions are extreme—50°C and 100 percent humidity. Even with special breathing apparatus and cooling suits explorers cannot endure much more than 30 minutes in the cave.


The Ionic Card Game3-2C Find Out ACTIVITY

How well do you understand the rules for naming and writing formulas for ionic compounds? Apply your knowledge and creativity to design a chemical card game.

Materials• pencils• felt markers• index cards

What to Do 1. Work with your group to design a card game that

involves naming and finding formulas for ionic compounds. Consider the following criteria as you design your game.

• Your game must include a variety of ions, including polyatomic ions, and must involve combining them to make a net charge of zero.

• The game must include at least 15 cards.

• You may base the game on other card games, or you may invent a new game entirely.

• The game should involve two to four players and require no more than 15 min to complete.

2. Prepare cards and a detailed set of rules for your game.

3. Try several rounds of your game within your group. Refine the rules as necessary.

4. Exchange games with at least one other group. After playing each game, complete an evaluation of the game as directed by your teacher.

5. As a class, devise a game you can play with all of the cards.

What Did You Find Out? 1. What challenges did your group face in designing and

producing the game?

2. How did your game differ from those of other groups?

3. What would you improve about your game if you were to redesign it? Give reasons for each change.

4. How has producing and playing a card game helped you to learn and practise naming rules and formula-writing rules for ionic compounds?




Chemical Formulas of Molecular Compounds

3-2D Think About It

Like ionic compounds, molecular compounds are represented by chemical formulas. How do chemical formulas of molecular compounds compare to chemical formulas of ionic compounds?

Selected Molecular Compounds

What to Do 1. Copy the table above. Be sure to leave plenty of room

in the far right column for drawing the molecular models.

2. Complete the columns with the headings “Elements present” and “How many atoms of each?”

3. Your teacher has provided molecular models for each of the compounds. Decide which model represents which compound and sketch the models to complete the table. Label each atom with the symbol of its element.

What Did You Find Out? 1. What do the chemical formulas of molecular

compounds represent?

2. Why is the chemical formula of hydrogen peroxide not simplified to HO?

3. How do formulas of molecular compounds differ from those of ionic compounds?

4. Water and hydrogen peroxide both contain hydrogen and oxygen. Yet they have different properties. Why do you think this is the case?

Chemical formula

H2O

H2O2

CO2

CO

C3H8

C6H12O6

Elements present

hydrogen, oxygen

How many atoms of each?

2 atoms H 1 atom O

Sketch of molecular modelName of substance

water

hydrogen peroxide

carbon dioxide

carbon monoxide

propane

glucose



Names and Formulas of Binary Molecular CompoundsChemical formulas of binary molecular compounds indicate how many atoms of each element are present in a single molecule of the compound, as shown for sulfur hexafluoride, SF6, in Figure 3.19. Like names for ionic compounds, names for binary molecular compounds have two parts—one for each element in the compound. The following three rules will help you write names and formulas of binary molecular compounds.

Rules for Writing Names and Formulas of Binary Molecular Compounds

1. The first element in the name and formula of a binary molecular compound is usually the one that is farther to the left on the periodic table. Example: In carbon monoxide, CO, carbon comes first because carbon is to the left of oxygen on the periodic table.

2. When naming, the suffix “–ide” is attached to the name of the second element. Example: “Oxygen” is changed to “oxide” in the name “carbon monoxide.”

3. When naming, prefixes are used to indicate how many atoms of each type are present in one molecule of the compound. Table 3.4 lists the first 10 prefixes. The prefix “mono-” is used only for the second element in the name. When there is no prefix, “mono-” is implied, as in “carbon monoxide.” Also, when “mono-” comes before “-oxide,” an "o" is dropped. Thus, you write “monoxide,” not “monooxide.”

Example: Using prefixes correctly, the name of CO is carbon monoxide.

Did You Know?

The difference between a molecule of carbon monoxide, CO, and carbon dioxide, CO2, is only one oxygen atom, but the difference in the properties of the compounds is a matter of life and death. Both are colourless, odourless gases, but you breathe in carbon dioxide all day with no ill effects. Air is 0.03% carbon dioxide and carbon dioxide is only lethal at 10%. Carbon monoxide, though, is lethal to humans in very small amounts—just 0.08%.

Figure 3.19 Because of its insulating properties, and because it does not react easily with other substances, sulfur hexafluoride is sometimes used to insulate double-glazed windows. The formula for sulfur hexafluoride, SF6, indicates that there is 1 sulfur atom and 6 fluorine atoms in each molecule of the compound.

Table 3.4 Prefixes Used to Name Binary Molecular Compounds

Prefix Number Prefix Number

mono- 1 hexa- 6

di- 2 hepta- 7

tri- 3 octa- 8

tetra- 4 nona- 9

penta- 5 deca- 10

binary molecular compound A compound composed of atoms of two different elements, usually two non-metals, that are joined together with covalent bonds



Sample Problem: Names and Formulas of Binary Molecular CompoundsProblemNitrogen and oxygen form a wide variety of different molecular compounds with different properties. Two examples are described below. A third is shown in Figure 3.20.(a) Dinitrogen tetraoxide is used in rocket fuels. What is its

formula?(b) NO2 is a toxic brown gas that is found in smog in urban areas.

What is its name?

Solution(a) Nitrogen comes first in the formula, as in the name, because

it is to the left of oxygen in the periodic table. The prefix “di” tells you that there are 2 nitrogen atoms and the prefix “tetra” tells you that there are 4 oxygen atoms.

The formula of dinitrogen tetraoxide is N2O4.(b) Follow these steps to name a compound.

The name of NO2 is nitrogen dioxide.

Check Your SolutionNitrogen is to the left of oxygen on the periodic table, so it appears first. The prefix “mono-” is implied in “nitrogen” and the prefix “di-” is correctly used in “dioxide.”

1. Name the leftmost element in the formula first.

2. Name the second element, making sure the name ends with the suffix “-ide.”

3. Add a prefix to each element’s name to indicate the number of atoms of each element in a molecule of the compound. If the first element would get the prefix “mono,” do not include that prefix.

The first element is N (nitrogen).

The second element is O (oxygen), which becomes “oxide.”

The compound’s name is nitrogen dioxide.

Practice Problems 9. Write the formulas of the following molecular compounds. (a) sulfur tetrafluoride (d) oxygen difluoride (b) disulfur difluoride (e) nitrogen tribromide (c) dinitrogen trioxide (f) diiodine hexachloride 10. Write the names of the following molecular compounds. (a) PI3 (c) SO3 (e) CCl4 (b) SO2 (d) S2F10 (f) N2O5

Figure 3.20 The compound NO acts to widen blood vessels, which can lessen chest pain in heart patients. The patient takes nitroglycerin pills, which react in the body to form NO. Apply What is the name of the compound NO?



Decisions, Decisions3-2E Think About It

Flowcharts can be used to represent a process graphically. For example, the simple flowchart to the right shows how to approach solving the problem of what to do when your morning alarm sounds. Although in practice you do not need a flowchart to decide whether or not to hit the snooze button, it can be helpful to use a flowchart to go through a more complex decision-making process. Writing a chemical name or formula, for example, requires making a number of decisions and determinations about the compound in question. How can you design flowcharts to represent the processes of naming and writing formulas for compounds?

What to Do 1. Work in small groups. Your teacher will assign you one

of the following two tasks:

• Design and make a flowchart to represent the process of naming compounds.

• Design and make a flowchart to represent the process of writing formulas for compounds.

2. In your group, brainstorm a list of criteria for your flowchart. What goal should it accomplish? Who should be able to use it? Have your teacher check and approve your criteria.

3. As a group, decide what medium you will use to present your flowchart. You could use software to create a digital image, for example, or you could draw your flowchart on a large sheet of paper.

4. As a group, design and make your flowchart. Test it by using it to name or write formulas for several ionic and molecular compounds.

5. Share your flowchart with the class.

What Did You Find Out? 1. Compare the naming flowcharts from different groups.

What were the similarities and differences? What worked and what did not work as well?

2. Compare the formula-writing flowcharts from different groups. What were the similarities and differences? What worked and what did not work as well?

3. How would you improve your flowchart if you had to redo this activity?

4. Would making a flowchart for these processes have been possible without a consistent, logical naming and formula-writing system? Explain your answer.

Morning alarm is going off

No

Yes

Yes

Is it summer,a weekend

or a holiday?

Get up and go to school.

Hit the snooze button.

No

Do you have a shift at work?

Get up and go to work.

IUPAC and Systematic NamesWhat comes to mind when you hear the word “lime”? You probably just pictured the small green citrus fruit shown in Figure 3.21. But lime is also the common name for a hugely important chemical with a broad variety of applications in farming, the pulp and paper industry, and the food industry, to name just a few. Chemists working with the compound lime know that it is an ionic compound composed of calcium and oxygen, but nothing about its common name suggests that fact. The name calcium oxide and the formula CaO, however, tell you what you need to know about the composition of lime.


Who developed the rules for naming and writing formulas that you have been learning to use? The international system for naming chemicals is maintained by the International Union of Pure and Applied Chemistry (IUPAC). Founded in 1919, IUPAC has developed a systematic method to name chemicals according to their composition. Today, scientists all over the world use the IUPAC system. This system ensures that each pure substance has a unique name, called its systematic name. The name of a substance describes its composition. It also enables scientists to write its chemical formula and predict some of its properties.

Figure 3.21 (A) The word “lime” could mean a tangy fruit. (B) Or, it could refer to the important industrial chemical calcium oxide, CaO. Common names are still used in industry and on labels, but they do not provide any information about the composition of the compound.Communicate What is another example of a word that can mean two different things?

A


Why IUPAC?3-2F Think About It

Bodies such as IUPAC and the ACS (American Chemical Society) create and uphold rules for naming elements and compounds. Before such rules were in place, however, chemicals were often given evocative names—now called common or “trivial” names—that emerged from their appearance, properties, production, or use rather than their chemical composition.

What to Do 1. Work in groups. Your teacher will assign you one of the

following names: alumina, cinnabar, hematite, laughing gas, limestone, magnetite, or slaked lime.

2. Conduct Internet research to find out the systematic name and chemical formula of your compound. List any additional names for the compound. Also, list some of its properties, applications, and a few interesting facts you come across in your research. If possible, find out the historical source of the common name.

3. Present your findings to the class as a poster or electronic slide presentation.

What Did You Find Out? 1. Was it always clear what compound was meant by the

common or “trivial” name? Explain your answer and give an example.

2. Give some advantages and disadvantages to using common names for substances.

3. What are the key advantages of having an international system of naming and writing formulas for chemical compounds? Are there any disadvantages?

B



Exceptions to the RulesOne important group of compounds breaks the naming rules given in this section. These are the compounds that contain hydrogen. You might think that HCl, for example, would be ionic. It contains hydrogen (found with the metals on the periodic table) and a non-metal. In fact, hydrogen is a non-metal, and HCl is known to be molecular. In its pure form, it is a gas at room temperature.

Although it is a molecular compound, HCl is not named in the same way as other molecular compounds you have encountered so far. Like other binary hydrogen-containing compounds, it is named as though it is an ionic compound. The correct name for HCl is thus hydrogen chloride, not hydrogen monochloride. Similarly, the name of H2S is hydrogen sulfide, not hydrogen disulfide. And these compounds are named differently when they are dissolved in water. You will learn more about this type of compound in Chapter 4.

Compounds containing hydrogen and carbon, such as ethane, C2H6, or ethanol, C2H5OH, have yet another set of naming rules, which you will encounter if you continue your studies in chemistry.

Key Naming Rules: A SummaryIn this section you learned how to name and write the formulas of ionic and molecular compounds. Table 3.5 below summarizes some of the key points to remember when naming molecular compounds and ionic compounds. In the next section, you’ll use your naming and formula writing skills to describe chemical reactions.

Table 3.5 A Summary of Key Naming and Formula-Writing Rules

Ionic Compounds Molecular Compounds

Binary Ionic Compounds

• The metallic element (positive ion) comes first in the name and the formula.

• The end of the name of the non-metallic element is changed to “-ide” (for example, sodium chloride).

• Ions of multivalent metals are named by adding Roman numerals in brackets to indicate their charges (for example, lead(IV) chloride).

• Subscripts in the formulas indicate the ratio of ions of each type in the compound.

• The total charge of the ions must add to zero.

Compounds with Polyatomic Ions

• Refer to Table 3.3 for the names and charges of polyatomic ions.

• When writing formulas, treat polyatomic ions as a unit. Include brackets around the formula of the ion if the ion as a whole takes a subscript.

Binary Molecular Compounds

• The leftmost element on the periodic table comes first in the name and the formula.

• The suffix "ide" is attached to the name of the second element.

• These compounds are named using prefixes to indicate the number of atoms in each molecule (for example, P2O5 is diphosphorus pentaoxide).

• The prefix “mono-“ is omitted in the first element named (e.g., CO2 is carbon dioxide).

• Subscripts in the formulas indicate the number of atoms of each element in each of the compound.

Did You Know?

Because of its very tiny size relative to other atoms, and its single electron, hydrogen is unusual. It has some properties that make it similar to the metals in Group 1, but others that make it similar to the non-metals in Group 17. For this reason, some periodic tables show hydrogen on its own, separated from the main groups.



Checking Concepts1. Jeremy states that nitrogen dioxide, NO2, is

not a binary compound because it contains three atoms in the molecule. Is Jeremy correct or incorrect? Explain your reasoning.

2. Why do people with diets that contain a lot of fish not suffer from goitres?

3. What ending do all binary compounds share, whether they are ionic or molecular compounds?

4. Fiona writes the formula for calcium chloride as Ca1Cl2. Is this correct? Explain why or why not.

5. The ratio of calcium to fluorine in calcium fluoride is 1:2. Based on this, can the ionic binary compound be written as Ca3F6? Explain why or why not.

6. Which of the following are binary compounds?

AlCl3, H2O, CNO, C6H12O6, MgS, PbF2, NaHCO3, NaOH

7. Write the names of the ionic compounds that form using the following elements.

(a) silver and chlorine (b) oxygen and zinc (c) beryllium and iodine (d) fluorine and magnesium

8. Identify the charge on the metallic ion in the following ionic compounds.

(a) PbO2

(b) CuS

(c) CrF3

(d) FeN9. A test question asks you to write the formula

for iron oxide. What further information do you need in order to write the compound’s formula, and how would this information be indicated in the question?

10. Mercury has the chemical symbol Hg and can form two ions when forming ionic compounds. Write and name the two possible compounds that could form when mercury combines with oxygen.

Understanding Key Ideas 11. Two sodium atoms are walking down the

street when one turns to the other and says, “I lost an electron.” The other says, “Are you sure?” The first one says, “Yes, I am positive.” Trailing behind is a magnesium atom, which proudly announces, “Hey, I am positive too.” Explain what the ions in this story are really telling us about the type of ion they form in ionic compounds.

12. Some people call the method of writing formulas for ionic compounds “electron accounting.” Explain why this is a good name.

13. David states that the name of CuCl2 is copper(I) chloride while Terri states that the name is copper(II) chloride. Which is correct? Explain your answer.

14. Write the formulas for each of the following: (a) iron(II) nitride (c) copper(I) sulfide (b) lead(II) oxide (d) tin(IV) fluoride 15. Write formulas for each of the following: (a) nitrogen dioxide (b) sulfur trioxide (c) dinitrogen tetraoxide (d) phosphorus pentachloride 16. Name each of the following: (a) AlPO4 (c) KHCO3 (b) Na2CO3 (d) Mg(OH)2 17. Write formulas for the following: (a) sodium sulfate (b) magnesium phosphate (c) calcium nitrate (d) aluminum chlorite 18. Write formulas for the following: (a) copper(I) chlorate (b) iron(II) phosphate (c) tin(IV) carbonate (d) nickel(II) permanganate

Consider the importance of using systematic names and formulas in the planning and analysis of a scientific investigation.

Project Prep


Loud explosions, flashes of colour, puffs of smoke—these are all results you might expect from chemical reactions. Many chemical reactions are explosive, colourful, and smoky. But many more take place in the world around you without your even noticing them. However, whether they are obvious or not, chemical reactions are vital to maintaining and sustaining your health and the health of all life on Earth. Table 3.6 shows some examples of chemical reactions.

In chemical terms, a chemical reaction occurs when one or more substances (elements or compounds) change to form one or more different substances (elements or compounds). The substances that undergo a chemical reaction are called the reactants. The substances formed in a chemical reaction are called products. Look at Table 3.6 and try to identify the products and reactants for each chemical reaction.

Key Termschemical reactionreactantproductchemical equationcoefficient

3.3 Chemical Equations and the Law of Conservation of Mass

What Do You Think?• How do elements and compounds interact to form different compounds?

• What relationship exists between the mass of substances before and after a

chemical change?

• What ways can you think of to represent a chemical change, and what are the

advantages and disadvantages of each?

reactant an element or compound that undergoes a chemical reaction

chemical reaction a process in which pure substances undergo a change, forming a different pure substances

product an element or compound that is formed in a chemical reaction

Table 3.6 Examples of Chemical Reactions

Example Description

lemon In a leavening reaction, baking soda reacts with cake rising lemon juice to form compounds including carbon dioxide and water.

fireworks In one of many reactions that take place in fireworks, exploding potassium chlorate reacts to form potassium chloride and oxygen.

oak tree In the reaction that is responsible for producing all performing of the oxygen in the air we breathe, plants use photosynthesis energy from the Sun to convert carbon dioxide and water into glucose and oxygen.

human Everything you do is powered by cellular respiration. performing In this energy-releasing reaction in the cells of your respiration body, oxygen and glucose are converted into carbon dioxide and water.




Figure 3.23 A word equation is one concise way to represent a chemical reaction. Identify What type of compound is the reactant? How would you classify the products?

productsreactant

“produces”or

“yields” “and”

ammonium nitrite nitrogen � water→

Investigation 3-3B: Mass Before and After

Suggested ActivityWord EquationsNitrogen and its compounds are an essential part of the biosphere. But too much nitrogen, or nitrogen in the wrong form, can damage an ecosystem. For example, too many ammonium-containing compounds in oceans or lakes can lead to an overgrowth of algae, as shown in Figure 3.22. The algae use up dissolved oxygen, killing other organisms, reducing diversity, and making the water unsafe for human use.

As part of a process that can be used to remove excess ammonium ions from wastewater, special bacteria can convert dissolved ammonium nitrite to gaseous nitrogen and liquid water. These bacteria are facilitating a useful chemical reaction.

Take a look at the description of a chemical reaction in the previous paragraph. Is there a more concise way to represent this chemical reaction? One way is to use the word equation shown in Figure 3.23. In a word equation, the name of each reactant is written to the left of an arrow and the name of each product is written to the right of the arrow. If there is more than one product or reactant they are separated by “” signs as shown.

Figure 3.22 (A) This algal bloom was caused by pollutants such as excess ammonium-containing compounds. (B) Ammonium-containing wastewater is produced by a variety of human activities, including farming, mining, and the food industry. (C) Certain bacteria can use a chemical reaction to clean up ammonium-containing wastewater.

A B C



The Conservation of Mass in Chemical ReactionsThe work of early chemists influenced the way chemical reactions are studied and represented today. In the late 1700s, a French scientist named Antoine Lavoisier, shown in Figure 3.24, greatly advanced the study of chemistry. One of his most influential contributions was recognizing the importance of measuring the mass of all the substances involved in a chemical change. These measurements were crucial for making accurate inferences about what happened to the substances.

Lavoisier performed many experiments in which he carefully measured the mass of the reactants, performed a reaction in a sealed container (a closed system), and then carefully measured the mass of the products. For example, he worked with mercury(II) oxide, HgO, which reacts to form mercury and oxygen when heated. Over and over again, his results were the same: the total mass of the reactants was the same as the total mass of the products. He summarized his results in his law of conservation of mass.

Conservation of Atoms

Lavoisier’s work allowed John Dalton to re-introduce the idea of atoms to the world in the early 1800s. Since atoms make up each reactant and product, Dalton’s atomic theory stated that each atom in the reactants is also present in the products. Since atoms are neither created nor destroyed in chemical reactions, the mass does not change, either.

In a chemical reaction, the total mass of the products is always the same as the total mass of the reactants.

The Law of Conservation of Mass

Figure 3.24 (A) Antoine and Marie-Anne Lavoisier were a successful scientific team. Marie-Anne translated scientific papers published in English into French for her husband and drew diagrams of the setups he used for his experiments. (B) Marie-Anne’s sketches include the closed system apparatus that Lavoisier used for his experiments that demonstrated conservation of mass.

A B


Chemical Equations and the Law of Conservation of MassScientists use a chemical equation to represent a chemical reaction. A chemical equation is different from a word equation in that it includes the formulas for the elements and compounds involved, rather than the names.

Skeleton equation Refer back to Figure 3.23. Replacing the words in a word equation with chemical formulas produces what is sometimes called a skeleton equation, shown below. A skeleton equation is still incomplete, however; it does not reflect the law of conservation of mass. There are different numbers of atoms of hydrogen and oxygen on each side of the equation.

NH4NO2 → N2 H2O

Balanced chemical equation A balanced chemical equation represents a chemical reaction as it really occurs. In accordance with the law of conservation of mass, atoms are never destroyed or created in a chemical reaction—they are just rearranged. So in a balanced chemical equation, the same number of atoms of each element appear on both sides of the arrow. This balance is achieved using coefficients. Coefficients not shown are assumed to be 1, as in this balanced chemical equation:

NH4NO2(aq) → N2(g) 2H2O(ℓ)

The State of a Substance

As shown in the example above, a chemical equation may also provide information about the states of the reactants and products in a chemical reaction. Table 3.7 shows the abbreviations used to do this.


Paper Clip Reactions3-3A Find Out ACTIVITY

In this activity, use paper clips to model atoms and molecules to help you balance chemical equations in accordance with the law of conservation of mass.

Materials• paper clips of different colours• list of skeleton equations

What to Do 1. Your teacher will give you a list of skeleton equations.

For each, use paper clips to model the reactants and products. One paper clip of a given colour should represent one atom of a given element. Note which colour you are using for each element.

2. Taking each equation in turn, work with the paper clip models to create a balanced equation in which the reactants have the same number of each colour of paper clip as the products.

What Did You Find Out? 1. What could you do to balance the equation while

maintaining an accurate model of the chemical reaction? What could you not do and still maintain an accurate model?

2. How did your paperclip models reflect the conservation of atoms in chemical equations?

3. What strategies did you use to make it easier to balance the equations?

4. Were any of the equations particularly easy to balance? Particularly difficult? Explain why you think this was the case.

Table 3.7 Abbreviations for States of Substances

State Abbreviation

Solid (s)

Liquid (ℓ)

Gas (g)

Dissolved in (aq) water (aqueous solution)

chemical equation a representation of a chemical reaction that uses chemical formulas and symbols

coefficient number placed in front of a chemical formula in a balanced equation to show how many atoms, molecules, or ions are involved



Balancing Chemical EquationsThe steps below summarize how to use coefficients to balance chemical equations. The explosive formation of water from hydrogen and oxygen, shown in Figure 3.25, is used to illustrate the steps.

Figure 3.25 A flame (A) is used to ignite a mixture of hydrogen (in the balloon) and oxygen in air. In the resulting explosion (B), water forms.

A

B

1. H2(g) O2(g) → H2O(ℓ)

In the skeleton equation, there is the same number of hydrogen atoms on both sides of the equation. There are more oxygen atoms in the reactants, however, than in the product.

Checking the Atom Balance

2. H2(g) O2(g) → 2H2O(ℓ)

Placing the coefficient 2 in front of H2O(ℓ) balances the oxygen atoms on each side of the equation. But now there are 4 hydrogen atoms on the product side and only 2 on the reactant side.


3. 2H2(g) O2(g) → 2H2O(ℓ)

Placing the coefficient 2 in front of H2(g) brings the total number of hydrogen atoms to 4 on each side of the equation. The equation is now balanced.


How to Balance a Chemical Equation

O2H2

H2O

2H2O

H2 O2

2H2O2H2O2

Element Reactant Product Equal?

H 2 4 no

O 2 2 yes


H 2 2 yes

O 2 1 no


H 4 4 yes

O 2 2 yes



Tips for Writing and Balancing Chemical EquationsWhen you are writing or balancing a chemical equation, it is important to remember that every equation is different. The same approach does not work for every chemical equation. You should be systematic, however, in the approach you use. A few suggestions to help you get started are listed below. Keep them in mind as you work through the Practice Problems on the next page.• Balance equations by adjusting coefficients, never by changing

chemical formulas.• Balance metals first.• Add coefficients to any elements last.• Balance hydrogen and oxygen last. They often appear in more than

one reactant or more than one product, so it is easier to balance them after the other elements are balanced.

• If a polyatomic ion appears in both a reactant and a product, treat it as a single unit.

• Once you think the chemical equation is balanced, do a final check by counting the atoms of each element one more time.

• If you go back and forth between two substances, using higher and higher coefficients, double-check each chemical formula. An error in a chemical formula might be preventing you from balancing the chemical equation.

• Remember that the following elements exist as diatomic molecules, like the one in Figure 3.26: hydrogen, H2(g), nitrogen, N2(g), oxygen, O2(g), fluorine, F2(g), chlorine, Cl2(g), bromine, Br2(ℓ), and iodine, I2(s).

Check Your Understanding 13. Iron reacts with oxygen to form iron(III) oxide. Write a word

equation to describe this reaction. 14. What was the significance of a closed system in Lavoisier’s

experiments? 15. What is the law of conservation of mass? 16. How does a balanced chemical equation reflect the law of

conservation of mass? 17. Determine the number of atoms of each element in the following

terms. (a) 3CO (d) 3PCl5 (b) H2O (e) 2NH4NO3 (c) 5NO2 (f) 2(NH4)2SO4 18. Balance each of the following chemical equations. (a) Mg(s) O2(g) → MgO(s) (b) Li(s) Br2(g) → LiBr(s) (c) Al(s) CuO(s) → Al2O3(s) Cu(s) (d) CH4(g) O2(g) → CO2(g) H2O(g) (e) Al(s) O2(g) → Al2O3(s) (f) CaCl2(aq) AgNO2(aq) → AgCl(s) Ca(NO3)2(aq)

Figure 3.26 When writing a chemical equation, always write oxygen as O2.Interpret Why would you not write oxygen as O in a chemical equation?



Figure 3.27 You may be familiar with the sharp smell of ammonia in glass cleaning products. Ammonia’s properties make it suitable for cleaning to a shine.

Sample Problem: Writing a Balanced Chemical EquationProblemAmmonia is an important fertilizer and is also used in household cleaners, as shown in Figure 3.27. In the industrial production of gaseous ammonia, gaseous nitrogen and gaseous hydrogen react to form the product. What is the balanced chemical equation?

Solution1. Begin by writing a word equation.

nitrogen hydrogen → ammonia2. Next, write a skeleton equation by writing the chemical formula

for each substance. Remember that nitrogen and hydrogen are diatomic molecules. Include the states.

N2(g) H2(g) → NH3(g)3. Finally, use coefficients to balance the equation. First consider the compound in the equation, since elements are

easier to balance later. You know you need to have 2 nitrogen atoms in the product to balance the nitrogen in the reactants. Therefore, add a coefficient of 2 to NH3(g).

N2(g) H2(g) → 2NH3(g) Now the nitrogen atoms are balanced. But the hydrogen atoms

are not balanced, because there are 2 hydrogen atoms on the reactant side and 6 hydrogen atoms on the product side. Therefore, add a coefficient of 3 to H2(g).

N2(g) 3H2(g) → 2NH3(g)

Check Your SolutionAll the chemical formulas are correct. The atoms all balance, as shown below.

Element

N

H

Reactant

2

6

Product

2

6

Equal?

yes

yes

Practice ProblemsFor each of the following reactions, write a word equation, a skeleton equation, and a balanced chemical equation, including states of matter. 11. Nitrogen monoxide gas reacts with oxygen gas to form

nitrogen dioxide gas. 12. Solid aluminum reacts with oxygen gas to form solid

aluminum oxide. 13. Potassium sulfate and silver nitrate, both dissolved in water,

react to form solid silver sulfate and dissolved potassium nitrate.



In this investigation, you will analyze the mass of products and reactants in a reaction that takes place when you mix two solutions.

QuestionHow does the mass of the reactants compare with the mass of the products in a chemical reaction between sodium hydroxide and iron(III) nitrate?

PredictionMake a prediction about how the mass of the reactants will compare to the mass of the products of the reaction you are about to perform.

Procedure 1. Read the steps that follow. Make a table to record your results.

2. Use a graduated cylinder to measure 20 mL of dilute sodium hydroxide solution, NaOH(aq). Pour the solution into the Erlenmeyer flask.

3. Pour the iron(III) nitrate solution, Fe(NO3)3(aq), into the small test tube. Fill the small test tube about half full.

4. Tilt the Erlenmeyer flask carefully and let the small test tube slide down inside, as shown in the photograph. Do not let the solutions mix. Seal the flask with the stopper.

5. Measure the mass of the flask and its contents. Record your measurement. Also record your qualitative observations about the appearance of the contents of the flask.

6. Tip the flask so that the solutions mix. Observe what happens and record your observations.

7. Measure the mass of the flask and its contents. Record your measurement.

8. Follow your teacher’s instructions to dispose safely of the materials and clean up your work area.

Analyze 1. What did you observe that tells you a chemical reaction took place?

2. The stoppered flask creates a closed system in which no substances can enter and from which no substances can escape. Why was it important to create a closed system for this investigation?

3. How did the mass of the reactants, flask, test tube, and stopper compare with their mass after the reaction?

Conclude and Apply 1. How did your results compare to the prediction you made at the beginning of

the activity?

2. Do you think you would see similar results if you carried out an investigation like this with different reactants (and different products)? Explain your answer.

3. Propose an explanation for what you observed in this investigation.

Mass Before and After3-3B

SkillCheck• Predicting

• Observing

• Recording

• Analyzing and Interpreting

Conduct an InVesTIgATIOn

Safety Precautions

• Wear safety eyewear throughout this activity.

• Wear a lab coat or apron throughout this activity.

• Rinse any spills with plenty of water, and report them to your teacher immediately.

• Dispose of materials as your teacher instructs.

Materials• graduated cylinder

• dilute sodium hydroxide solution, 0.1 mol/L NaOH(aq)

• 200 mL Erlenmeyer flask

• dilute iron(III) nitrate solution, Fe(NO3)3(aq)

• small test tube

• stopper (to fit the Erlenmeyer flask)

• balance



Green Chemistry The development of new medicinal drugs has great benefits for humans and other animals. The chemical reactions that are used to make these drugs, however, often involve many steps. These steps may result in as much as 100 000 times more waste than the amount of drug produced, by mass. The waste can harm the environment, and disposal of waste can be expensive.

A relatively new field of chemistry, called green chemistry, focusses on designing reactions that produce less waste. These reactions can be used for drug manufacturing and other industrial processes. Green chemistry also aims to reduce or eliminate toxic substances that are used in or produced by many chemical reactions. Some of the principles of green chemistry include:

• preventing or reducing waste

• using safer solvents

• using renewable raw materials

• ensuring that reactions are energy efficient

Green Medicine As one example, Merck and Co. Inc. has developed a greener reaction for synthesizing a drug called Emend®. This drug is used to treat vomiting and nausea caused by chemotherapy. The new reaction is far more efficient than the original reaction. It uses smaller amounts of reactants, water, and energy to produce twice as much of the desired product! It also involves fewer steps than the original reaction. The costs of producing the drug are therefore reduced.

In the past, chemists who were working to protect the environment designed ways to clean up the toxic wastes produced by chemical processes. The goal of green chemistry is not to create these toxic wastes in the first place.

%AE ( mass of final desired chemical compound ________________________________ sum of masess of all reactant compounds

) 100%

400 000350 000300 000250 000200 000150 000100 00050 000

0

Litr

esof

Was

te p

er 1

000

kgof

Em

end®

Pro

duce

d

Using GreenChemistry

Before GreenChemistry

Reduction of Waste with Green Chemistry

Atom economy (AE) is an important principle of green chemistry. Chemists design reactions to use as little of the reactants as possible to produce the greatest yield of the desired product. Waste is therefore reduced. Chemists calculate percent atom economy using this equation:

The process that involves green chemistry produces 340 000 fewer litres of waste per 1000 kg of drug produced compared to the traditional process. This is a huge reduction in waste: 340 000 L of waste could fill more than 2000 average-sized bathtubs!

Questions

1. Turn to Appendix B at the end of in this textbook and read the 12 principles of green chemistry. Choose one principle. Explain how this principle helps to protect the environment.

2. Rewrite each of the 12 principle statements for a class of Grade 7 students so they will be able to understand the principles of green chemistry.



Checking Concepts1. Write word equations for three common

reactions. Label the products and the reactants.

2. When looking at an equation for a chemical reaction, what does the arrow mean?

3. Describe the difference between a word equation and a chemical equation.

4. What is a skeleton equation, and how does it differ from a balanced chemical equation?

5. When a chemical compound must be placed in water to form a solution in a reaction, how is this indicated in the chemical equation?

6. Identify the reactants and products in each of the following:

(a) Mg(s) HCl(aq) → MgCl2(aq) H2(g) (b) Fe(s) O2(g) → Fe2O3(s) (c) Na3PO4 FeCl3 → FePO4 NaCl (d) MgO(s) → Mg(s) O2(g)

7. Describe the contribution of Antoine Lavoisier to the study of chemical reactions.

8. What are the numbers that are placed in front of a chemical compound to balance a chemical reaction called?

9. Which elements exist as diatomic molecules?

Understanding Key Ideas10. As a tree gets older, it increases in mass.

Explain why this is not an exception to the law of conservation of mass.

11. Your classmate states that the law of conservation of mass is not being followed in the reaction of Mg(s) O2(g) → MgO(s) because there is a loss of one atom of oxygen in the process. Is this statement correct or incorrect? Explain your answer.

12. After balancing the reaction of hydrogen gas and oxygen gas to form water vapour, a student balanced the reaction as follows:

4H2(g) 2O2(g) → 4H2O(g) Is this balanced correctly? Explain your

answer.13. State the number of atoms of each element in

the following terms: (a) 2NH4NO2 (c) 3Cu2(SO4) (b) 5H2SO4 (d) 4FeCl3

14. Write the skeleton equation for each of the following reactions:

(a) sodium chlorate reacts with potassium iodide to form sodium iodide and potassium chlorate

(b) copper(II) sulfate reacts with heat to form carbon dioxide gas and copper(II) oxide

(c) zinc reacts with copper(II) nitrate to form copper and zinc nitrate

(d) iron reacts with oxygen to form iron(III) oxide

15. Which equation from question 14 is not balanced? Determine the balanced equation for this reaction.

16. Propane, C3H8, reacts with oxygen to form carbon dioxide and water during the combustion process.

(a) Write the skeleton equation for this reaction.

(b) Balance the reaction. 17. Write balanced chemical reactions for each

word equation. (You do not need to include states.)

(a) potassium iodide → potassium iodine (b) lead(II) nitrate sodium chloride →

lead(II) chloride sodium nitrate (c) magnesium silver nitrate → magnesium nitrate silver (d) sodium water →

sodium hydroxide hydrogen 18. Balance the following skeleton equations: (a) H2O2(aq) → H2O(ℓ) O2(g) (b) Fe(s) H2SO4(aq) → H2(g) Fe2(SO4)3(aq) (c) FeBr3(s) → FeBr2(s) + Br2(ℓ)

Consider the importance of including balanced chemical equations as part of the planning and analysis of a laboratory investigation.

Project Prep



Prepare Your Own SummaryIn this chapter, you learned how to name and write formulas for chemical compounds. You also learned how to write balanced chemical equations to represent chemical reactions. Create your own summary of the key ideas from this chapter. You may include graphic organizers or illustrations or both for your summary. (See Appendix B for help with using graphic organizers.) Use the following headings to organize your summary: 1. Ionic and Molecular Compounds 2. Names and Formulas of Ionic and Molecular

Compounds 3. Chemical Equations and the Law of

Conservation of Mass

Checking Concepts 1. You are probably familiar with the smell of

chlorine from visiting a local swimming pool. (a) Explain why chlorine compounds are

added to pool water. (b) After heavy use, municipalities will

“shock” the water in a pool by adding a larger than normal amount of chlorine. Why would this be done?

2. How are ionic compounds and molecular compounds different at the atomic level?

3. Describe three physical properties of ionic compounds and three physical properties of molecular compounds.

4. When given the compound S2O5 to name, Maya said it was called disulfur pentaoxide while Dennis said that it was called pentaoxygen disulfide. Who is correct and why?

5. Consider the order of elements in formulas of ionic compounds.

(a) In a binary ionic compound, which element is listed first in the formula, the positively charged metallic ion or the negatively charged non-metallic ion?

(b) Is the order the same when writing the name of the compound?

6. What are the small numbers located in some compound formulas called, and what do they indicate?

7. Write the ionic compound formulas for each of the following combinations of atoms.

(a) aluminum and chlorine (b) lithium and oxygen (c) sulfur and magnesium (d) nitrogen and calcium 8. Write names for each of the following: (a) SO3 (b) N2O5 (c) PCl3 (d) P2O3 9. Explain the steps that must be followed to

determine the formula of calcium nitride. 10. Consider the chemicals that react and form

in chemical changes. (a) What is the general name given to

chemical compounds that are required to start a chemical reaction?

(b) What is the general name given to the chemical compounds that form during a chemical reaction?

11. What is a multivalent metal? Give three examples as part of your answer.

12. When you see a Roman numeral in the name of an ionic compound, what does it tell you about the metal in the compound?

13. What is the ratio of lithium ions to oxide ions in lithium oxide?

14. Explain how balancing a chemical equation reflects the law of conservation of mass.

Understanding Key Ideas 15. Is a family unit more like an ionic compound

or a molecular compound? Explain your answer.

16. Explain why a binary ionic compound cannot be formed with lithium and calcium.

17. Determine the charge for each metallic ion in the following compounds:

(a) CuSO4 (c) TiO2 (b) CrF3 (d) Fe2S3

C h a p t e r3



18. In which of the following compounds does iron have a 2 charge?

FeS, Fe3(PO3)2, Fe(OH)2, FeN, FeSO4, Fe(CH3COO)2, Fe(OH)3

19. Write formulas for each of the following: (a) tetraphosphorus hexoxide (b) dinitrogen monoxide (c) sulfur tetrafluoride (d) carbon disulfide 20. Write names for each of the following: (a) SnO (c) Fe2S3 (b) PbCl2 (d) NiN 21. Write the formulas of each of the following: (a) iron(II) carbonate (b) tin(IV) chromate (c) ammonium phosphate (d) copper(I) acetate 22. Octane, C8H18, is used in fuels for

automobiles. In the combustion process, octane combines with oxygen to produce carbon dioxide gas and water vapour.

(a) Identify the reactants and products in this process.

(b) Write the skeleton equation for this reaction.

(c) Balance the skeleton equation. 23. Write skeleton equations for the following

reactions. (You do not need to include states.)

(a) calcium sulfate potassium hydroxide →calcium hydroxide potassium sulfate

(b) barium water → barium hydroxide hydrogen

(c) copper(I) sulfide oxygen → copper(I) oxide sulfur dioxide

(d) magnesium nitride water → magnesium oxide nitrogen trihydride

24. Balance the skeleton equations from question 23.

25. Balance the following skeleton equations. (a) NO2(g) O2(g) 2H2O(ℓ) → HNO3(aq) (b) CH4(g) O2(g) Cl2(g) → HCl(g) CO(g)

(c) Mg(OH)2(s) HNO3(aq) → Mg(NO3)2(aq) H2O(ℓ) (d) Na2S(aq) HBr(aq) → NaBr(aq) H2S(g) 26. For each of the following reactions, write a

word equation, a skeleton equation, and a balanced chemical equation, including states of matter.

(a) Nitrogen gas reacts with bromine gas to form gaseous nitrogen tribromide.

(b) Liquid phosphorus trichloride reacts with chlorine gas to form solid phosphorus pentachloride.

(c) Aqueous silver nitrate reacts with solid copper to form aqueous copper(II) nitrate and solid silver.

27. Baking soda, NaHCO3(s), and citric acid, C6H8O7(s), react in water to form carbon dioxide, water, and sodium citrate, Na3C6H5O7(aq). This is the reaction you observed if you did the Launch Lab at the beginning of the chapter.

(a) Sodium citrate is an ionic compound. What is the charge on the negative ion? How do you know?

(b) Write a skeleton equation for the reaction.

(c) Write a balanced chemical equation for the reaction. Include states of matter.

The law of conservation of mass states that matter is not destroyed or created in a chemical reaction—it stays constant. How does the law of conservation of mass relate to the three Rs: reduce, reuse, and recycle? How does it relate to the principles of green chemistry, described in the Science Watch in Section 3.3? Since the quantity of matter on Earth is more or less constant, what implications does the law of conservation of mass have for the way we use natural resources such as oil and gas?

Why It Matters


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