chapter sixteen: compounds

Chapter Sixteen: Compounds16.1 Chemical Bonds and

Electrons16.2 Chemical Formulas16.3 Molecules and Carbon

Compounds

16.1 Chemical Bonds and Electrons

A chemical bond forms when atoms transfer or share electrons.

A covalent bond is formed when atoms share electrons.

16.1 Chemical formulasA molecule’s chemical formula tells you the ratio of atoms of each element in the compound.

16.1 Ionic bondsNot all compounds are made of

molecules.Ionic bonds are bonds in which

electrons are transferred from one atom to another.

Sodium and chlorine form an ionic bond because the positive sodium ion is attracted to the negative chloride ion.

16.1 Why chemical bonds formIt takes energy to

separate atoms that are bonded together.

The same energy is released when chemical bonds form.

Atoms form bonds to reach a lower energy state.

16.1 ReactivityIn chemistry, reactive means an element readily forms chemical bonds, often releasing energy.

Some elements are more reactive than others.

The closer an element is to having the same number of electrons as a noble gas, the more reactive the element is.

16.1 Valence electronsChemical bonds are formed only between

the electrons in the highest unfilled energy level.

These electrons are called valence electrons.

16.1 Valence electrons and the periodic table

Going from left to right across a period each new element has one more valence electron than the one before it.

How many valence electrons does nitrogen have?

16.1 Valence electrons and the periodic table

Oxygen combines with one beryllium atom because beryllium can supply two valence electrons to give oxygen its preferred number of 8.

16.1 Valence electrons and the periodic table

Carbon has four valence electrons. Two oxygen atoms can bond with a

single carbon atom, each oxygen sharing two of carbon’s four valence electrons.

The bonds in carbon dioxide (CO2) are double bonds because each bond involves 2 electrons.

16.1 Lewis dot diagramsA clever way to keep

track of valence electrons is to draw Lewis dot diagrams.

A dot diagram shows the element symbol surrounded by one to eight dots representing the valence electrons. What is the dot

structure for nitrogen?

16.2 Chemical Formulas and Oxidation Numbers

All compounds have an electrical charge of zero (they are neutral).

An oxidation number indicates the charge on the atom (or ion) when electrons are lost, gained, or shared in chemical bonds.

16.2 Oxidation NumbersA sodium atom

always ionizes to become Na+ (a charge of +1) when it combines with other atoms to make a compound.

Therefore, we say that sodium has an oxidation number of 1+. What is chlorine’s oxidation number?

16.2 Ionic bondsOn the periodic table, strong electron donors are the left side (alkali metals).

Strong electron acceptors are on the right side (halogens).

The further apart two elements are on the periodic table, the more likely they are to form an ionic compound.

16.2 Covalent bondsCovalent compounds form when elements have roughly equal tendency to accept electrons.

Elements that are both nonmetals and therefore close together on the periodic table tend to form covalent compounds.

16.2 Oxidation numbers and chemical formulas

Remember, the oxidation numbers for all the atoms in a compound must add up to zero.

16.2 Oxidation numbers

Some periodic tables list multiple oxidation numbers for most elements.

This is because more complex bonding is possible.

Solving ProblemsIron and oxygen combine to form a compound. Iron (Fe) has an oxidation number of 3+. Oxygen (O) has an oxidation number of 2–.

Predict the chemical formula of this compound.

1. Looking for: …formula for a binary compound

2. Given … Fe3+ and O2–

3. Relationships: Write the subscripts so that the sum of the

oxidation numbers equals zero.4. Solution

Two iron atoms = 2 × (3+) = 6+ Three oxygen atoms = 3 × (2–) = 6–

Solving Problems

16.2 Polyatomic ionsCompounds can contain more than two elements.

Some of these types of compounds contain polyatomic ions.

A polyatomic ion has more than one type of atom.

The prefix poly means “many.”

16.2 Some polyatomic ions

Solving ProblemsAl3+ combines with sulfate (SO4)2– to make aluminum sulfate.

Write the chemical formula for aluminum sulfate.

1. Looking for: …formula for a ternary compound

2. Given … Al3+ and SO4

2–

3. Relationships: Write the subscripts so that the sum of the

oxidation numbers equals zero.4. Solution

Two aluminum ions = 2 × (3+) = 6+ Three sulfate ions = 3 × (2–) = 6–

Solving Problems

17.2 Formula massThe sum of the atomic mass values of the atoms in a chemical formula is called the formula mass.

17.2 Avogadro’s NumberThe Avogadro number was named in

honor of Amedeo Avogadro who discovered that a mole of any gas under the same conditions has the same number of molecules.

Johann Josef Loschmidt, a German physicist, named and discovered the Avogadro number.

Loschmidt realized that a mole of any substance—be it a gas, liquid, or solid—contains 6.02 x 1023 atoms or molecules.

17.2 Molar MassThe mass (in grams) of one mole of a compound is called its molar mass.

What is the molar mass of one mole of CaCO3?

1. Looking for: … molar mass of CaCO3

2. Given … chemical formula

3. Relationships: no. amu in formula = molar mass in

grams

Solving Problems

4. SolutionSolving Problems

Formula mass CaC03 = 100.19 g1 mole CaC03 = 100.19 g

CaCO3

16.3 Molecules and Carbon Compounds

In addition to the elements from which it is made, the shape of a molecule is also important to its function and properties.

We use structural diagrams to show the shape and arrangement of atoms in a molecule.

16.3 Structural Diagrams

3096P class only

16.3 Structural diagramsTwo substances have the same formula

as aspirin, but not its pain relieving properties.

16.3 The chemistry of carbon Carbon molecules come in three basic

forms: straight chains, branching chains, and rings.

All three forms are found in important biological molecules.

16.3 Organic compoundsOrganic chemistry is the branch of

chemistry that specializes in carbon compounds, also known as organic molecules.

Plastic, rubber, and gasoline are important carbon compounds.

Scientists classify the organic molecules in living things into four basic groups: carbohydrates, proteins, fats, and nucleic acids.

16.3 Carbohydrates Carbohydrates

are energy-rich compounds made from carbon, hydrogen, and oxygen.

Carbohydrates are classified as either sugars or starches.

16.3 Carbohydrates Carbohydrates are

mainly composed of carbon, hydrogen, and oxygen in a ratio of about 1:2:1.

Glucose, C6H12O6, is a simple sugar.

Table sugar is a carbohydrate called sucrose.

16.3 Carbohydrates Starches are

long chains of simple sugars joined together.

Cellulose is the primary molecule in plant fibers, including wood.

16.3 Lipids Like

carbohydrates, lipids are energy-rich compounds made from carbon, hydrogen, and oxygen whose ratio is much less than 1:2:1.

Lipids include fats, oils, and waxes.

16.3 Saturated or unsaturated fat?In a saturated fat,

carbon atoms are surrounded by as many hydrogen atoms as possible.

An unsaturated fat has fewer hydrogen atoms than it could have.

16.3 Proteins Proteins are basic molecular building

blocks of cells and all parts of animals.

Proteins are among the largest organic molecules.

Why is the shape of aprotein important?

16.3 EnzymesEnzymes are proteins.

An enzyme is a type of protein that cells use to speed up chemical reactions in living things.

16.3 ProteinsProtein molecules are made of smaller molecules called amino acids.

Your cells combine different amino acids in various ways to make new and different proteins.

16.3 Nucleic AcidsNucleic acids are compounds made of long, repeating chains called nucleotides.

Each nucleotide contains:

1. a sugar molecule

2. a phosphate molecule, and

3. a base molecule.

16.3 DNA and nucleic acidsDNA is a nucleic

acid .A DNA molecule is

put together like a twisted ladder.This model shows a short piece of the flattened DNA ladder.A DNA molecule is usually twisted and much longer.

16.3 DNAEach side of the ladder is made of: 5-carbon sugars

called deoxyribose

and phosphate groups.

16.3 DNAThere are four nitrogen bases in two matched pairs.