An ionic compound is
composed of a positive part (typically a metal) and a negative part (typically
a nonmetal). In writing and naming a binary ionic compound such as NaCl, the
metal (Na) comes first, and the nonmetal (Cl) comes second. The full name of the
metal is used and -ide is added to the nonmetal as a suffix. NaCl is therefore
called sodium chloride.
Most metal-nonmetal binary compounds are classified as ionic compounds. There are two kinds of
situations:
1. Binary ionic compounds in which the metal element has a fixed oxidation number : The metals
in groups IA and IIA and aluminum in group IIIA always have only one oxidation
number (+1, +2, and +3, respectively). Naming binary ionic compounds containing
these metals is rather straight-forward as the oxidation states of the metals
need not be specified. For example, LiCl2 is lithium chloride, and
MgO is called magnesium oxide. Notice that the full name of the metals (lithium
and magnesium) are given, and the suffix -ide is added to the names of the
nonmetals (chlorine and oxygen).
2. Binary compounds
containing metals of variable oxidation numbers: Often a compound contains a
metal that can have more than one oxidation state. Many transition metals, for
example, have two oxidation states. In such cases, the state of the metal in
the given compound must be specified. There are two systems that are commonly
used to designate the particular oxidation state of the metal:
The Stock method.
Currently, this is the most common method used. In this method the oxidation
state of the metal is listed with Roman numerals in parentheses after the name
of the element. For example, the compound CuF is named copper (I) fluoride, and
the compound CuF2 is named copper (II) fluoride.
The classical method. In
this older method, the name of the metal is modified with the suffixes -ous
(for the lower oxidation number) and -ic (for the higher oxidation number) to
distinguish between the two. Using this method, the compound CuF would be
called cuprous fluoride, and CuF2 would be called cupric fluoride.
When the series has more
than two compounds, such as H2O and H2O2, the
prefix per is used to distinguish oxygen’s –1 oxidation state from its –2
state. Therefore H2O2 is called hydrogen peroxide.
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