sCIeNCePS 5.6.2 Compare and contrast characteristics of physical and chemical properties.PS 5.7.1 Explain how a small number of naturally- occurring elements can result in the arge variety of substances found in the world. PS 5.7.2 Create models of common compounds: water, carbon dioxide, salt, iron oxide, ammonia.PS 5.7.3 Identify compounds as substances consisting of two or more elements chemically combined PS 5.7.4 Compare and contrast properties of compounds to those of the elements that compose them: salt: sodium chloride; water: hydrogen, oxygen; carbon dioxide: carbon, oxygenPS 5.7.6 Classify substances as elements, compounds, mixtures.PS 5.8.4 Create atomic models of common elements.
mathM 13.6.2 Determine which unit of measure or measurement tool matches the context for a problem situation.
LaNGUaGe artsOV 2.6.2 Establish purpose for listening.OV 2.7.2 Establish purpose for listening OV 2.8.2 Establish purpose for listening.
s objeCtIvesThe students will learn:
objeCtIve #1 To define compounds.
objeCtIve #2 To describe the difference between covalent and ionic compounds.
objeCtIve #3 To cite examples of covalent and ionic compounds.
objeCtIve #4 To create models of water molecules.
objeCtIve #5 To contrast and compare properties of compounds to those of the elements that created them.
objeCtIve #6 To appropriately use verbal speaking skills in class discussion with the teacher and Garden Program Specialist.
Page 4 EARTH SYSTEMS • Everything Matters, Part 2: Teachers’ Guide
LessoN pLaN
I. Start in the classrooma. Icebreaker
Ask the students: “What is the most abundant compound on Earth?”
ANSWER: “Water, which can also be called H2O.”
b. present main topic▲s Explain compounds and the difference between covalent and
ionic bonds.
meets objeCtIves #1,2, 5
▲s Using the images provided as visuals, describe the molecular structure of various compounds. Explain the chemical symbols, including the use of subscripts to identify the number of atoms in each molecule.
meets objeCtIves #3,5
II. Take class to the garden▲s Take toothpicks and protractors to garden. ▲s Point to a source of water nearby (puddle, irrigation hose, rain
barrels.). Explain that water is a compound, a substance created by two pure elements, oxygen and hydrogen. Describe how elements form compounds by sharing or losing and gaining electrons. Define covalent and ionic.
meets objeCtIves #1–2
▲s Instruct students to make models of water and salt molecules as explained on the “Supporting Information for Teachers” pages. Point out that compounds have very different properties compared to the original elements that join to create compounds.
meets objeCtIves #4–5
▲s Plant, harvest and work in the garden following the Garden Guide.
III. Take class back to classroom▲s Hand out the Student Workbook as reference material and class
assignment. Review take it home activities and encourage students to do them.
EARTH SYSTEMS • Everything Matters, Part 2: Teachers’ Guide Page 5
sUpportING INFormatIoN For teaChers
baCkGroUNd
By using everyday items from the kitchen and garden, students can build basic molecular models, which will help foster their understanding of covalent and ionic compounds.
Bonds are the forces that hold atoms together. Covalent bonds share their electrons. In ionic bonds, one of the atoms will lose an electron, where as the other atom will gain that electron.
Covalent bonds are liquid or gaseous at room temperature where as ionic bonds are normally solid.
Another difference in the two types of bonds is that a covalent bond has a low boiling point, where as the ionic bond has a high boiling point.
The types of bonds are very important to understand and will give the students a building block of knowledge that they will use to master chemistry concepts.
aCtIvIty 1
Build a model illustrating a water molecule, a covalent compound.
materials needed▲s Cherry tomatoes and peas (picked from the
garden) ▲s Toothpicks▲s Protractor (optional)
Note: If fresh produce is not available, alternative materials such as raisins, jelly beans, dried beans
or mini marshmallows may be used. The items should be of two different sizes to represent the larger oxygen atoms and the smaller hydrogen atoms.
procedure
Instruct students to make a ball-and-stick model, using one cherry tomato to represent the larger oxygen atom and two peas for the smaller hydrogen atoms. Insert one end of a toothpick into a pea and the other end into a tomato so they are firmly attached. The hydrogen atoms should form an angle of 104.5°. Use the protractor to measure. ▲✚ Optional: Make a space-filling molecule by
breaking the toothpicks in half and pushing them far enough into the peas and tomatoes that the “atoms” touch.
eNrIChmeNt aCtIvIty
For a more advanced model of atoms, one could use Styrofoam balls and toothpicks. The students can color and label their atoms. Be sure to use protractors to represent accurate angles.
study guide for studentsdid you have a glass of water today? Scientifically speaking, water is a compound. It is not a pure element (a substance that consists of only one type of atom), but a combination of atoms. In this case, the pure elements oxygen and hydrogen have joined together to form water. In doing so, they created a new substance. It does not have the same properties as the original elements of oxygen and hydrogen on their own. It’s a substance in its own right. Now, oxygen and hydrogen molecules can’t just come together willy-nilly to form water. They always have to come together in exactly the right proportion: one oxygen molecule and two hydrogen molecules. That is true whether you have one drop of water or one gallon. There are more compounds that exist in the universe than elements because elements are combines to form a numerous amout of compounds.
One more note about compounds. They can be covalent or ionic. When atoms team up, they either share or lose/gain electrons.
Covalent Compounds
You recall that electrons are the little particles with an electric charge that buzz around the nucleus. Think of this as a shell that has room for one (or several) more electron(s). A water molecule consists of two hydrogen atoms and one oxygen atom. Each hydrogen atom has room for one more electron around its nucleus and the oxygen atom has room for two more electrons around its nucleus. So they share electrons from each other. They bond by forming a very tight structure that has become a water molecule. When a compound is formed as a result of atoms sharing electrons, it is considered covalent. The chemical formula is written as H2O. a subscript ( the 2 in the H2O) is only used when more than one atom is being represented. For example, in H2O there are (2) Hydrogen and (1) Oxygen.
EARTH SYSTEMS • Everything Matters, Part 2: Study Guide Page 2
Another example of a covalent compound is carbon dioxide, CO2, a gas in our atmosphere. It consists of one carbon atom and two oxygen atoms that share a total of eight electrons. You already know something about oxygen. Carbon is considered the magic element for almost everything on earth. All living things contain carbon.
Ionic Compounds
Atoms don’t only share electrons, they lose them or gain them. When that happens,
the compound is considered ionic. Sodium chloride, commonly known as table salt, is a good example. It forms when chlorine (Cl) and sodium (Na) atoms combine. (Notice that even though one element is chlorine, the resulting compound is chloride.) The sodium atom loses an electron, which the chlorine atom takes up. Now with one electron less than protons, the sodium atom is considered positively charged. The opposite is true for the chlorine atom. It now has one electron more than protons and is considered negatively charged. What happens when you bring negatively and positively charged things together? They attract each other and form a new substance—like table salt. Salt forms as a crystal, not a single molecule. Next time you sprinkle some on your eggs, remember it as an example of an ionic compound. Its formula is written as NaCl.
Image of a salt crystal:
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
(natrium chloride)covalent bond the bond that forms when atoms share electrons
ionic bond the bond that forms when atoms gain or lose electrons
compound pure substance produced when two or more elements combine whose properties are different from the elements from which it is formed
element – a pure substance that is made of only on kind of atom
subscript numbers used to describe how many atoms of an element are present in a chemical formula
1. what’s the difference between an element and a compound? Element: pure element, not a combination
Compound: combination of different elements
2. are there more elements or more compounds that exist in our universe? why?More compounds, because elements are combined to form a numerous amount of compounds.
3. what do you call compounds that share electrons?b. Covalent
3. what do you call compounds that lose/gain electrons?c. Ionic
PS 5.7.4 Compare and contrast properties of compounds to those of the elements that compose them: salt: sodium chloride; water: hydrogen, oxygen; carbon dioxide: carbon, oxygen
1. what’s the difference between an element and a compound?
2. are there more elements or more compounds that exist in our universe? why?
3. what do you call compounds that share electrons?a. Saturated
b. Covalent
c. Ionic
d. Dependent
3. what do you call compounds that lose/gain electrons?a. Independent
b. Unsaturated
c. Ionic
d. Covalent
Take it HomePretend you are a covalent bond and “share” a walk with a friend or family
1. what’s the difference between an element and a compound? Element: pure element, not a combination
Compound: combination of different elements
2. are there more elements or more compounds that exist in our universe? why?More compounds, because elements are combined to form a numerous amount of compounds.
3. what do you call compounds that share electrons?b. Covalent
3. what do you call compounds that lose/gain electrons?c. Ionic
PS 5.7.4 Compare and contrast properties of compounds to those of the elements that compose them: salt: sodium chloride; water: hydrogen, oxygen; carbon dioxide: carbon, oxygen
1. what’s the difference between an element and a compound?
2. are there more elements or more compounds that exist in our universe? why?
3. what do you call compounds that share electrons?a. Saturated
b. Covalent
c. Ionic
d. Dependent
3. what do you call compounds that lose/gain electrons?a. Independent
b. Unsaturated
c. Ionic
d. Covalent
4. on the back of this paper, describe in your own words what happens when a hydrogen and an oxygen molecule join.
Take it HomePretend you are a covalent bond and “share” a walk with a friend or family
1. what’s the difference between an element and a compound? Element: pure element, not a combination
Compound: combination of different elements
2. are there more elements or more compounds that exist in our universe? why?More compounds, because elements are combined to form a numerous amount of compounds.
3. what do you call compounds that share electrons?b. Covalent
3. what do you call compounds that lose/gain electrons?c. Ionic
4. on the back of this paper, describe in your own words what happens when a hydrogen and an oxygen molecule join.Answers will vary. Hydrogen and oxygen elements combine to form a compound that is water. The answer may also include that there are two hydrogen molecules and one oxygen molecule, and that is is a covalent bond, meaning they share electrons.
