Chapter 7 – Chemical Formulas
& Compounds
I. Chemical Names and
Formulas
• All natural and synthetic substances have
chemical names, however, most substances are
better known by common names
Chemical Name
Common Name
Calcium carbonate
Limestone
Sodium chloride
Table salt
Dihydrogen monoxide Water
Sodium bicarbonate
Baking soda
Acetic acid
Vinegar
Nitrous oxide
Laughing gas
• A. Significance of a Chemical Formula
• 1. Chemical formula – indicates the number
of atoms of each element in a compound
• 2. Molecular formula – the number of
atoms of each element in a single molecule
• a. Octane – C8H18
• b. Octane is a hydrocarbon, which means it
is a molecular compound made of carbon
and hydrogen only
Methane
Ethane
Propane
Butane
Benzene
• 3. Formula unit – the simplest ratio of cations and
anions in an ionic compound
• a. Sodium chloride – NaCl
• b. Aluminum sulfate – Al2(SO4)3
• c. Potassium hydroxide – KOH
• B. Monatomic Ions
• 1. Monatomic ions – ions formed from a single
atom
• 2. A monatomic cation is named the same name as
the element
• 3. A monatomic anion uses the first part of the
element’s name, but drops the last part of the name
and adds the suffix -ide
• C. Binary Ionic Compounds
• 1. Binary compounds – compounds
composed of only two elements
• 2. In a binary compound, the total number of
positive charges must equal the total number
of negative charges; therefore, the formula
unit is neutral
• 3. The binary compound is named by using
its cation name first and its anion name
second
Sodium chloride
• 4. Use the following steps to write the formula for
binary ionic compounds:
• a. Write the symbol for the cation first
• b. Write the symbol for the anion second
• c. Use superscripts to write the charge of each ion
• d. check to see if the charges balance out to zero
• e. If the charges balance to zero, then the formula
unit will simply be the two elements’ symbols
with no subscripts
• f. If the charges do not balance out to zero, then
use the anion’s charge as a subscript for the cation,
and the cation’s charge as a subscript for the
anion, and this becomes the formula unit
• D. Naming Binary Ionic Compounds
• 1. Nomenclature – refers to the naming
system used to name the compound
• 2. Stock system – a naming system using
Roman numerals to indicate the charge of
the cation
• a. Some metals (transition metals) can form
two or more cations
• b. Roman numerals are enclosed in
parenthesis and written right after the name
of the cation
FeCl2 - Iron (II )chloride
Fe2O3 - Iron (III) oxide
• E. Compounds Containing Polyatomic Ions
• 1. Ionic compounds may contain more than just
two elements, in which case, they contain a metal
and a polyatomic ion (NaOH – sodium hydroxide)
• 2. If the polyatomic ions contain oxygen, then it is
called an oxyanion (SO4
NH4)
• 3. The oxyanion may contain one or more oxygen
atoms (CO3-2 carbonate or CO2-2 carbonite)
• a. the oxyanion with the greater number of
oxygen atoms has a suffix ending of –ate
• b. the oxyanion with the smaller number of
oxygen atoms has a suffix ending of -ite
• c. If it contains one less than the –ite anion,
it is given the prefix of hypo- (CO-2 hypocarbonite)
• d. If it contains one more than the –ate ion,
it is given the prefix of per- (CO4-2 percarbonate)
• 4. The method for writing formulas with
polyatomic ions is the same as with binary
compounds, except the polyatomic ion name
will be the cation or anion name
• a. polyatomic ions with positive charges are
cations and are written first Ex. (NH4+1)
• b. polyatomic ions with negative charges are
anions and are written second
• c. if a subscript must be given to a
polyatomic ion in a formula, then the
polyatomic ion is placed in parenthesis first
• F. Naming Binary Molecular Compounds
• 1. The new naming system is the Stock
system, which uses oxidation numbers
• 2. The older system uses prefixes to indicate
the number of each atom in the molecule
• Mono (1) Di(2) Tri(3) Tetra(4) Penta(5) Hexa(6)
• Hepta(7) Octa(8) Nona(9) Deca(10)
• G. Covalent Network compounds
• 1. Some covalent compounds do not have
individual molecules, but instead, all the
molecules are joined into a network (similar
to ions in a crystal)
• 2. The subscripts in the formula represent
the smallest whole number ratio of atoms
• H. Acids and Salts
• 1. Binary acids – acids that
• consist of two elements
(HCl)
• (hydrogen and a halogen)
• 2. Oxyacids – acids made of hydrogen, oxygen,
and another nonmetal (hydrogen and a
polyatomic ion)
(H2SO4)
• Our use of the term acid really
• means the acidic compound dissolved in water
• 4. Hydrochloric acid is hydrogen chloride
dissolved in water
• 5. Salt – a cation and an anion from an acid
• 6. Some anions have the word
• hydrogen or the prefix bi- added
• to their name (bicarbonate)
• I. Naming Acids
• 1. If the –ate form of the polyatomic ion is used in
the acid, then the acid’s name ends in –ic
• 2. If the –ite form of the polyatomic ion is used in
the acid, then acid’s name ends in –ous
• 3. If the hypo- or per- forms of the polyatomic
ion are used in the acid, then the acid’s name
includes the prefixes
• Examples: sulfate – sulfuric acid
•
sulfite – sulfurous acid
•
perchlorate – perchloric acid
•
hypochlorite – hypochlorous acid