Naming Compounds
and
Writing Formulas
Chapter 2 (2.6 and 2.7)
Writing Names for Ionic Compounds
• Write the name of the cation followed
by the name of the anion
• Ending of monatomic anions must be
changed to –ide
• Include Roman numerals for metals
that have variable charges
• Groups 1 & 2, Al, Zn, Ag, Cd do not
need Roman Numerals
Naming Hydrates
• The ONLY time that you use the
numerical prefixes with ionic
compounds is to indicate the number of
water molecules attached to a hydrated
ionic compound
CuSO4 . 5H2O
copper (II) sulfate pentahydrate
Oxides
2(O )
• Metals and nonmetal combine with
oxygen to form oxides
• Examples: CaO is calcium oxide
PtO2 is platinum (IV) oxide
Peroxides (O2
2-)
• Active metals (group 1 except Li,
group 2 except Be & Mg) may combine
with oxygen to form peroxides
• Each oxygen is 1• Example: CaO2 is calcium peroxide
• H2O2 is hydrogen peroxide; H can act
as an active metal
Superoxides (O2
-)
• Very active metals (K, Rb, Cs)
may combine with oxygen to
form superoxides
• Each oxygen is -1/2
• Example: RbO2 is rubidium
superoxide
Name these Oxides
• KO2
• potassium superoxide
• K2O2
• potassium peroxide
• K2O
• potassium oxide
Names and Formulas for
Binary Molecular Compounds
• Binary molecular compounds contain two
elements.
• The most metallic element (i.e., the one farthest
to the left on the periodic table) is usually
written first. Exception: NH3 (ammonia)
• If both elements are in the same group, the
lower one is written first. Example: SO2
• Greek prefixes (page 63) are used to indicate the
number of atoms (mono, di, tri).
• The first letter is omitted when o-o or a-o
combinations occur.
• The prefix mono is never used with the first
element (Example: carbon monoxide, CO).
Examples:
Cl2O
dichlorine monoxide
N2O4
dinitrogen tetroxide
NF3
nitrogen trifluoride
P4S10
tetraphosphorus decasulfide
Writing empirical formulas for
ionic compounds
• You must combine cations and
anions in a ratio so that the total
positive charge is equal to the
total negative charge
• Use the criss cross method
Binary Ionic Compounds
• Contain atoms of two elements
• Write the chemical formula by using the
criss cross method
CaI2
Subscripts must be reduced since an
empirical formula shows the lowest whole
number ratio of ions or atoms
Ca2O2 must be reduced to CaO
Ternary Ionic Compounds
• Contain atoms of
three elements
• Parentheses must be
placed around
polyatomic ions to
separate the ion from
the subscript when
more than one ion is
needed
Ca(OH)2
Charges of Ions
Group
1
2
3
15
16
17
Charge
1+
2+
3+
321-
Names and Formulas of Acids
• The names of acids are related to the names
of anions:
• -ide becomes hydro- ...-ic acid;
HCl
hydrochloric acid
• -ate becomes –ic acid;
HClO4 perchloric acid
• -ite becomes –ous acid.
HClO
hypochlorous acid