Chapter 18
Chemical Bonds
1. Stability in Bonding
a. When elements combine they form compounds. These compounds often have new
properties that are not like the individual elements themselves.
b. When two elemental symbols are put together they make up the formula of the
compound; i.e. NaCl.
i. Chemical Formula – shows what elements a compound contains and the
exact number of the atoms of each element in a unit of that compound.
ii. Common compounds, include, sand (SiO2), vinegar (CH3COOH), battery
acid (H2SO4), and stomach acid (HCl)
c. An atom is chemically stable when its outer energy level is complete. Hydrogen and
Helium are stable with two electrons, while noble gases are happy with eight
electrons in their outer level.
d. When atoms, gain, lose, or share electrons, an attraction forms between the atoms. A
chemical bond is the force that holds atoms together in a compound.
2. Types of Bonds
a. An ion is a charged particle that either has more or fewer electrons than protons.
i. When an atom loses electrons, it becomes a positive ion called a cation
ii. When an atom gains an electron, it becomes a negative ion called an anion.
b. An ionic bond is the force of attraction between the opposite charges of the ions in an
ionic compound.
i. The number of positive charges must equal that of the negative charges.
ii. Ionic bonds are formed between metals and nonmetals.
iii. The charge on the whole ionic compound must equal zero (neutral)
c. A covalent bond is the attraction that forms between atoms when they share
electrons.
i. The neutral particle that forms is called a molecule
ii. Covalent bonds are formed between nonmetallic elements
iii. Covalent bonds can form multiple bonds, such as double and triple bonds.
d. A nonpolar bond is a covalent bond in which electrons are shared equally by both
atoms, usually between similar or identical atoms.
e. A polar bond is a bond in which electrons are shared unequally, resulting in a slightly
positive end and a slightly negative end.
f.
A polar molecule is one of unequal sharing of electrons
g. A nonpolar molecule is a molecule that does not have oppositely charged ends.
3. Writing Formulas and Naming Compounds
a. An oxidation number is a positive or negative number that indicates
i. For an ionic compound, the oxidation number is the same as the charge on
the ion.
b. Binary compounds are composed of two element.
c. Rules for writing formulas
i. Write the symbol of the element that has the positive oxidation number or
charge
ii. Write the symbol of the element with the negative oxidation number
iii. Find the least common multiple of the charges of each ion. The charge of the
ion because the subscript of the second ion.
d. A polyatomic ion is a positively or negatively charge, covalently bonded group of
atoms.
i. Polyatomic ions contain two are more elements.
ii. Some common polyatomic ions are: (Table 4, pg. 569)
1. Ammonium (NH4+1)
2. Hydroxide (OH-1)
3. Sulfate (SO4-2)
4. Nitrate (NO3-1)
e. A hydrate is a compound that has water chemically attached to its atoms and written
into its chemical formula.
Chapter 18 Vocabulary
Binary Compound – compound that is composed of two elements.
Chemical Bond – force that holds atoms together in a compound.
Chemical Formula – chemical shorthand that uses symbols to tell what elements are in a compound and
their ratios
Covalent Bond – attraction formed between atoms when they share electrons.
Hydrate – compound that has water chemically attached to its atoms and written into its chemical
formula.
Molecule - a neutral particle that forms as a result of electron sharing among atoms
Nonpolar Bond – a covalent bond in which electrons are shared equally by both atoms.
Nonpolar Molecule – molecule that shares electrons equally and does not have oppositely charged ends.
Oxidation Number – positive or negative number that indicates how many electrons an atom has gained,
lost, or shared to become stable.
Polar Bond – a covalent bond in which the electrons are not shared equally, resulting in a slightly
positive end and a slightly negative end.
Polar Molecule – a neutral molecule in which unequal electron sharing results in a slightly positive end
and a slightly negative end.
Polyatomic ion – positively or negatively charged, covalently bonded group of atoms.