Molecules, Ions and Their Compounds

Chemistry 101

Chapter 3

Virginia State University

Dr. Victor VilchizSummer 2008

Chemical compounds are classified as organic or inorganic.

Organic compounds are compounds that contain carbon combined with other elements, such as hydrogen, oxygen, and nitrogen; they do not contain metals.

Inorganic compounds are compounds composed of elements other than carbon and usually contain at least one metal atom.

Chemical Substances; Formulas and Names

• Naming simple compounds

An important class of molecular substances that contain carbon is the organic compounds.

Organic compounds make up the majority of all known compounds.

The simplest organic compounds are hydrocarbons, or compounds containing only hydrogen and carbon.

Common examples include methane, CH4, ethane, C2H6, and propane, C3H8.

Chemical Formulas; Molecular Substances

• Organic compounds

A covalent compound as we said before is formed by sharing electrons between 2 nonmetals or metalloids.

These compounds are usually molecular and are named using a prefix system.

When naming these compounds name the element further to the left (in the periodic table) first, then the one on the right.

Naming Covalent Compounds

You name the first element using the exact element name.

Name the second element by writing the root of the element’s name and add the suffix “–ide.”

If there is more than one atom of any given element, you add the Greek prefix denoting how many atoms of that element are present. Table lists the Greek prefixes used.

If only one atom of the second element is present it gets the prefix “mono”

Naming Covalent Compounds

Here are some examples of prefix names for binary molecular compounds.

PF5 phosphorus pentafluoride

SO2 sulfur dioxide

SF6 sulfur hexafluoride

N2O4 dinitrogen tetroxide

CO carbon monoxide

Naming Covalent Compounds

Acids are traditionally defined as compounds that could donate an H+; however, they are acids only in the presence of water. In other words before they enter the liquid they are covalent compounds and they are NOT acids.

There are two main types of acids:Binary acids consist of a hydrogen ion and any single anion. For example, HCl is hydrochloric acid.

An oxoacid is an acid containing hydrogen, oxygen, and another element. An example is a HNO3, nitric acid. (see Figure 2.23)

Naming Acids

Naming Acids

• Binary Acids– Start with the prefix “Hydro” which represents the

Hydrogen, followed it with the root of the name of the second element and append the ending –oic acid.

• Oxoacids– Use the root of the “E” element if the ion taking part in

the acid had an ending in –ate to the root append the ending –ic acid, if it ends on –ite then append the ending –ous acid. If the ion had a prefix use the same prefix.

Naming Acids

• Examples:– HCl(g) Hydrogen Chloride– HCl(aq) HydroChloric Acid– H2S(g) Dihydrogen Sulfide– H2S(aq) HydroSulfic Acid– H3PO4(aq) Phosphoric Acid– HClO4(aq) Perchloric Acid– HClO(aq) Hypochlorous Acid

Ionic Compounds Formulas

• How do we know how many atoms of each ion we need?– A simple crossing of the charges can answer that question about

90% of the time.• Example: Mg2+ and PO4

3-

Mg3(PO4)2

Check the charges… 3 x (+2) = +6 2 x (-3) = -6

– When they combined they cancel to yield a neutral compound.

Ionic Compounds Formulas

• The crossing technique does not work if the magnitude of the charges is the same

• Example: Mg2+ and CO32-

Mg2(CO3)2

This is incorrect since we want the lowest ratio possible which is 1:1 to yield MgCO3

Ionic Compounds Properties

• Ionic compounds have properties completely different from their component elements.– Example: Table Salt (NaCl)

• Sodium (Na) in the presence of water reacts violently heating up the water and producing hydrogen if the temperature of the water is high enough the hydrogen can ignite explosively.

• Chloride (Cl) Green poisonous and corrosive gas. If inhaled will destroy the nasal passages then dissolve in the stomach producing high concentration of hydrochloric acid which will destroy the stomach lining producing ulcers.

• Salt (NaCl) posses none of the properties mentioned above.

Ionic Structure

•Ions form a 3-D lattice.

•The coulombic (electrostatic) attraction is so high that in order to separate one ion from the lattice requires a lot of energy (Hlatt).

•The lattice energy depends on charge and size of the ions.

Lattice Energy

• Since the lattice energy is an electrostatic interaction the more separated the charges are the weaker the interaction is.– Bigger ions have lower lattice energies

• The higher the charge of the ions the stronger they will attract ions of the opposite charge.

• When size and charge point to opposite trends the charge will outweigh the size.– From smallest atom to biggest atom there is only 1.7x factor. From

a +1 to +2 that is already a 2x factor.

12

21

r

qqH latt

Properties of Ionic Substances

• Dues to the charged interaction a blow to a crystal leads to the possibility of splitting the crystal since we will force like charged particles to interact.

• Ionic compounds have high melting/boiling points since in order to move the ions from their respective spots it will require breaking the lattice.

Ionic Solutions

• However, if we do melt an ionic compound it will be able to conduct current.

• When ionic compounds are placed in a solvent the produced solution conducts electricity. The higher the number of ions the higher the conductivity.

• More when we cover chapter 4.

A hydrate is a compound that contains water molecules weakly bound in its crystals.

Hydrates are named from the anhydrous (dry) compound, followed by the word “hydrate” with a Greek prefix to indicate the number of water molecules per formula unit of the compound.

For example, CuSO4. 5H2O is known as

copper(II)sulfate pentahydrate. (see Figure 2.24)

Naming Hydrates

Determining Chemical Formulas

• Determining both empirical and molecular formulas of a compound from the percent composition.

The percent composition of a compound leads directly to its empirical formula.

An empirical formula (or simplest formula) for a compound is the formula of the substance written with the smallest integer (whole number) subscripts.

Determining Chemical Formulas

• The percent composition of a compound is the mass percentage of each element in the compound.

We define the mass percentage of “A” as the parts of “A” per hundred parts of the total, by mass. That is,

%100whole the of mass

whole in A"" of mass A"" % mass

Mass Percentages from Formulas

• Let’s calculate the percent composition of butane, C4H10.

First, we need the molecular mass of C4H10.amu 48.0 amu/atom 12.0 @ carbons 4 amu 10.0 amu/atom 1.00 @ hydrogens 10

amu 58.0 HC of molecule 1 104

Now, we can calculate the percents.C%8.82%100 C % total amu 0.58

C amu 48.0

H%2.17%100 H % total amu 0.58H amu 10.0

Determining Chemical Formulas

• Determining the empirical formula from the percent composition.

Benzoic acid is a white, crystalline powder used as a food preservative. The compound contains 68.8% C, 5.0% H, and 26.2% O by mass. What is its empirical formula?

In other words, give the smallest whole-number ratio of the subscripts in the formula

Cx HyOz

Determining Chemical Formulas

• Determining the empirical formula from the percent composition.

For the purposes of this calculation and making calculations simpler, we will assume we have 100.0 grams of sample benzoic acid.

Then the percentage of each element equals the mass of each element in the sample.

Since x, y, and z in our formula represent mole-mole ratios, we must first convert these masses to moles.

Determining Chemical Formulas

C mol )3(73.5g 12.0C mol 1

C g 8.68

H mol 0.5g 1.0H mol 1

C g 0.5

O mol)7(63.1g 16.0O mol 1

O g 2.26

This isn’t quite a whole number ratio, but if we divide each number by the smallest of the three, a better ratio might emerge.

Determining the empirical formula from the percent composition.

Our 100.0 grams of benzoic acid would contain:

Determining Chemical Formulas

Determining the empirical formula from the percent composition.

Our 100.0 grams of benzoic acid would contain:

3.501.63(7)C mol 73.5

3.01.63(7)H mol 0.5

1.001.63(7)O mol )7(63.1

now it’s not too difficult to see that the smallest whole number ratio is 7:6:2. The empirical formula is C7H6O2 .

Determining Chemical Formulas

• Determining the “true” molecular formula from the empirical formula.

An empirical formula gives only the smallest whole-number ratio of atoms in a formula.

The “true” molecular formula could be a multiple of the empirical formula (since both would have the same percent composition).

To determine the “true” molecular formula, we must know the “true” molecular weight of the compound.

Determining Chemical Formulas

• Determining the “true” molecular formula from the empirical formula.

For example, suppose the empirical formula of a compound is CH2O and its “true” molecular weight is 60.0 g/mol.The molar weight of the empirical formula (the “empirical weight”) is only 30.0 g/mol.This would imply that the “true” molecular formula is actually the empirical formula doubled 2(CH2O) or

C2H4O2

Molecular and structural formulasand molecular models.

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A model of a portion of a Sodium Chloride crystal.

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Common Ions of the transition metals

List of Polyatomic Ions

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Greek Prefixes for Covalent Compounds Nomenclature

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Making and Acid

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Molecular model of nitric acid.

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Figure 2.24: Copper (II) sulfate. Photo courtesy of James Scherer.

Return to Slide 44

Naming Flow Chart

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Naming Flow Chart II

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Naming Acids Flow Chart

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Quantities of Quantities of Reactants and Reactants and

ProductsProductsChapter 4Chapter 4

Dr. Victor Vilchiz

What is a mole?What is a mole?

• A A molemole is a unit of measurement is a unit of measurement used to specified amounts of used to specified amounts of chemical substances.chemical substances.– It is It is notnot a unit of mass. a unit of mass.– It is similar to “a dozen”It is similar to “a dozen”

•A dozen eggs is not the same as a dozen A dozen eggs is not the same as a dozen cars but they are still both a dozen.cars but they are still both a dozen.

What is a mole?What is a mole?

• A A molemole is defined as the number is defined as the number of atoms of carbon in 12 g of of atoms of carbon in 12 g of Carbon-12. Carbon-12. (examples)(examples)

• 1mole=6.022x101mole=6.022x102323 atoms and can atoms and can be applied to any moietybe applied to any moiety– 6.022x106.022x102323 is also known as is also known as

Avogadro’s Number (NAvogadro’s Number (NAA))• 1mol of Carbon=12g Carbon = 6.022x101mol of Carbon=12g Carbon = 6.022x102323 C atoms C atoms

• 1mol of water= 18g H1mol of water= 18g H22O =6.022x10O =6.022x102323 water molecules water molecules

Why the mole?Why the mole?

• The mole helps determine amounts The mole helps determine amounts of substances and allows for of substances and allows for conversion between species.conversion between species.– CaCOCaCO33(s) + 2HCl(aq) (s) + 2HCl(aq) CaCl CaCl22(aq) + H(aq) + H22COCO33(aq)(aq)

• From this we cannot say 1g of CaCOFrom this we cannot say 1g of CaCO33 will react with 2 will react with 2 grams of HCl; however, we can say 1mol of CaCOgrams of HCl; however, we can say 1mol of CaCO33 reacts reacts with 2 moles of HCl.with 2 moles of HCl.

– 1 mole of CaCO1 mole of CaCO33 is not the same as 1 mole of HCl mass is not the same as 1 mole of HCl mass wise, but both have 6.022x10wise, but both have 6.022x102323 molecules. molecules.

Molar Mass ExamplesMolar Mass Examples

• Molar Mass of Ca(CMolar Mass of Ca(C22HH33OO22))22, Calcium , Calcium Acetate.Acetate.2x(40.1)+4(12.0)+6(1.01)+4(16.0)=198.3g/2x(40.1)+4(12.0)+6(1.01)+4(16.0)=198.3g/

molmol• Molar Mass of Ethylene Glycol, CMolar Mass of Ethylene Glycol, C22HH44OO22..

2x(12.0)+4(1.01)+2(16.0)=60.0g/mol2x(12.0)+4(1.01)+2(16.0)=60.0g/mol• Molar Mass of Ammonium Oxalate, Molar Mass of Ammonium Oxalate,

(NH(NH44))22CC22OO44..2x(14.0)+8x(1.01)+2(12.0)+4(16.0)=124.12x(14.0)+8x(1.01)+2(12.0)+4(16.0)=124.1

g/molg/mol

Stoichiometry: Stoichiometry: Quantitative Relations in Quantitative Relations in Chemical ReactionsChemical Reactions•StoichiometryStoichiometry is the is the

calculation of the quantities calculation of the quantities of reactants and products of reactants and products involved in a chemical involved in a chemical reaction.reaction.

It is based on the balanced chemical It is based on the balanced chemical equation and on the relationship between equation and on the relationship between mass and moles.mass and moles.

Such calculations are fundamental to Such calculations are fundamental to most quantitative work in chemistry.most quantitative work in chemistry.

A chemical equation is the symbolic representation of a chemical reaction in terms of chemical formulas.

For example, the burning of sodium and chlorine to produce sodium chloride is written

The reactants are starting substances in a chemical reaction. The arrow means “yields.” The formulas on the right side of the arrow represent the products.

Chemical Reactions: Chemical Reactions: EquationsEquations

• Writing chemical equationsWriting chemical equations

NaCl2ClNa2 2

In many cases, it is useful to indicate the states of the substances in the equation.

When you use these labels, the previous equation becomes

s=solid, l=liquid, g=gas, aq=aqueous

Chemical Reactions: Chemical Reactions: EquationsEquations

• Writing chemical equationsWriting chemical equations

)s(NaCl2)g(Cl)s(Na2 2

Molar Interpretation of Molar Interpretation of a Chemical Equationa Chemical Equation• A balanced chemical equation:A balanced chemical equation:

22HH22 + +11OO22 22HH22OO

can be interpreted to read 2 moles of can be interpreted to read 2 moles of Hydrogen react with one mole of Hydrogen react with one mole of oxygen to produce 2 moles of water.oxygen to produce 2 moles of water.– In the balanced equation the In the balanced equation the 2, 1, and 22, 1, and 2

are known as the stoichiometric are known as the stoichiometric coefficients.coefficients.• At the molecular level they refer to the number of At the molecular level they refer to the number of

molecules reacting.molecules reacting.

Molar Interpretation of a Molar Interpretation of a Chemical EquationChemical Equation

Because moles can be converted to Because moles can be converted to mass, you can also give a mass mass, you can also give a mass interpretation of a chemical equation.interpretation of a chemical equation.

22HH22 + +11OO22 22HH22OO

2(2.02g)H2(2.02g)H22 react with 1(32.0g) O react with 1(32.0g) O22 to yield to yield 2(18.0g)H2(18.0g)H22OO

4.04g H4.04g H22 react with 32.0g O react with 32.0g O22 to yield 36.0g to yield 36.0g HH22OO