Chapter Sixteen: Compounds
16.1 Chemical Bonds and
Electrons
16.2 Chemical Formulas
16.3 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 formulas
A molecule’s chemical formula tells
you the ratio of atoms of each
element in the compound.
16.1 Ionic bonds
Not 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 form
It 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 Reactivity
In 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 electrons
Chemical 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 diagrams
A 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
What is the dot
valence electrons.
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 Numbers
A 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 bonds
On 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 bonds
Covalent 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 Problems
Iron 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.
Solving Problems
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–
16.2 Polyatomic ions
Compounds 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 Problems
Al3+ combines with sulfate (SO4)2– to
make aluminum sulfate.
Write the chemical formula for
aluminum sulfate.
Solving Problems
1. Looking for:
 …formula for a ternary compound
2. Given
 … Al3+ and SO42–
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–
17.2 Formula mass
The sum of the atomic mass values of
the atoms in a chemical formula is
called the formula mass.
17.2 Avogadro’s Number
The 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 Mass
The mass (in grams) of one mole of a
compound is called its molar mass.
Solving Problems
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. Solution
Formula mass CaC03 = 100.19
g
1 mole CaC0 = 100.19 g
3
CaCO
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 diagrams
Two 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 compounds
Organic 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 energyrich 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 a
protein important?
16.3 Enzymes
Enzymes are
proteins.
An enzyme is a
type of protein that
cells use to speed
up chemical
reactions in living
things.
16.3 Proteins
Protein 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 Acids
Nucleic acids are compounds made
of long, repeating chains called
nucleotides.
Each nucleotide
contains:
1.
2.
3.
a sugar
molecule
a phosphate
molecule, and
a base
molecule.
16.3 DNA and nucleic acids
DNA 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 DNA
Each side of the
ladder is made of:
 5-carbon sugars
called deoxyribose
 and phosphate
groups.
16.3 DNA
There are four
nitrogen bases in
two matched pairs.