Rules for Naming Compounds
Ionic Compounds (a compound of a metal and non-metal)
Most of the Time:

the name of the metal comes first (with the first letter capitalized) and the name of the
non-metal comes second (without any capitalization)

add the suffix "-ide" to the end of the name of the non-metal
(ie. sulfur becomes sulfide)

examples: KBr = Potassium bromide; MgS = Magnesium sulfide; CaI2 = Calcium iodide
Exceptions to the Rule:
 if the metal is a transition metal, the rules change
 transition metals are metals that can form more than one kind of ion
 transition metals can create elements that have multiple ionic charges
 transition metals include elements with atomic number included in the ranges: 21-30,
39-48, 72-80, and 104-112
 name these the same as any ionic compound, except after the metal, indicate the
charge of the metal with Roman numerals in brackets
 examples: FeO = Iron (II) oxide because oxygen has a -2 charge and so would require a
+2 charge from the iron; Fe2O3 = Iron (III) oxide because the 3 oxygen ions with a -2
charge (total of -6) and the 2 irons would need to have a -3 charge to balance out the
oxygen
Polyatomic Ions (an ion made up of two or more atoms that act as a group in bonding)
Here are some common polyatomic ions:
Polyatomic Name
hydroxide
chlorate
chromate
acetate
nitrate
nitrite
hydrogen carbonate
(bicarbonate)
carbonate
sulfate
phosphate
ammonium
Formula
OHClO3CrO42C2H3O2NO3NO2-
Ionic Charge
112111-
HCO3-
1-
CO32SO42PO43NH4+
2231+
 rules for writing the formulas of polyatomic compounds is similar to ionic
compounds, except place parentheses around the polyatomic ion
 naming polyatomic compounds: same rules as ionic compounds but don't add "-ide" to
the polyatomic compound
 example: CuCO3 = Copper (II) carbonate because we know that the charge for
carbonate is -2, our charge for copper must be +2
Molecular Compounds (a compound of two non-metals)





the name of the binary molecular compound (one made of only two different elements)
ends with the suffix "-ide"
the name of the compound begins with the element that has the greater combining
capacity
use a prefix to specify the number of atoms of each element that is present in the
molecule. The prefix "mono-" is only used for the second element and the "o" is
dropped in the case of oxygen.
prefixes include: mono (1); di (2); tri (3); tetra (4); penta (5); hexa (6)
examples: CO = carbon monoxide; CO2 = carbon dioxide;
P2S5 = Diphosphorous pentasulfide
Diatomic Molecules (a molecule that contains two identical atoms)


seven elements form compounds in this way: Hydrogen, Nitrogen, Oxygen, Flourine,
Chlorine, Bromine, and Iodine
examples: H2 = hydrogen gas; O2 = oxygen gas