| Naming Inorganic Compounds |
Naming Inorganic Compounds
Scientists have established a system of rules for
naming most inorganic substances
Elements
The names of metals generally end in -ium
or -um (examples are sodium, potassium, aluminum, and magnesium). The
exceptions are metals that were used and named in ancient times, such as iron,
copper, and gold. The names of nonmetals frequently end in -ine, -on,
or �gen (such as iodine, argon, and oxygen). Given the names of the
constituent elements and common ions, most of the common inorganic compounds can
be named using the rules presented below.
Acids
The names of acids without oxygen in the molecule
have the prefix hydro- (sometimes shortened to hydr-) and the
suffix -ic attached to the stem based on the names of the constituent
elements (other than hydrogen). For example, HCl (made of hydrogen and chlorine)
is hydrochloric acid; HBr (made of hydrogen and bromine) is hydrobromic acid; HI
(made of hydrogen and iodine) is hydroiodic acid; HCN (made of hydrogen, carbon,
and nitrogen) is hydrocyanic acid; and H2S (made of hydrogen and
sulfur) is hydrosulfuric acid.
Names of acids containing oxygen (known as
oxoacids) are derived from the number of oxygen atoms in the
molecules of a series, or class, of acids. An example of an oxoacid series is as
follows: HClO, HClO2, HClO3, HClO4. If a class
of acids contains only one member, its name is given the suffix �ic. For
example, H2CO3 is carbonic acid. If an acid series
contains two acids, such as H2SO4 and H2SO3,
the acid containing more oxygen atoms is given the suffix �ic, while the
acid with fewer oxygen atoms is given the suffix �ous. For example, H2SO4
is sulfuric acid, and H2SO3 is sulfurous acid.
Similarly, HNO3 is nitric acid, and HNO2 is nitrous acid.
In the case of an extensive acid series (such as HClO, HClO2, HClO3,
HClO4), the acid with the fewest oxygen atoms is given the prefix
hypo- and the suffix �ous, and the acid with the most oxygen atoms is
given the prefix per-. In the above example, HClO is hypochlorous acid,
HClO2 is chlorous acid, HClO3 is chloric acid, and HClO4
is perchloric acid.
Positive Ions
Names of positive ions end in -ium if the
ion has only one oxidation state (only one level of net charge). For example,
the positive ion of
ammonia is NH4+ (ammonium), and the positive ion of
water (H2O) is H3O+ or H+ (hydronium).
If two oxidation states (two levels of net charge) exist for the positive ion of
an element, the less positive ion ends in �ous, and the more positive ion
ends in -ic. For instance, the two positive ions of copper are Cu+
(cuprous) and Cu2+ (cupric). The oxidation state of a
positive ion can also be designated by placing a Roman numeral after the name of
the element. These positive ions of copper can also be written as copper (I) and
copper (II), respectively.
Negative Ions
Names of negative ions from oxygen-deficient
acids (for more information, see the Acids section of this article) end
in �ide. For example, Cl- (chloride) from HCl, and CN-
(cyanide) from HCN. Names of negative ions derived from acids with the -ous
prefix end in -ite. For example, NO2- (nitrite) is
derived from HNO2 (nitrous acid), and SO32-
(sulfite) is derived from H2SO3 (sulfurous acid).
Salts
Salts are named for the ions that compose them.
The cation (positively charged ion) within the compound is named first.
Examples are NaCl (sodium chloride), BaO (barium oxide), Fe(NO3)2
[iron (II) nitrate], and Fe(NO3)3 [iron (III) nitrate].
Covalent Compounds
If two elements form a covalent compound, the
prefixes di-, tri-, tetra-, penta-, hexa-,
and so on, are used to indicate the number of atoms. Examples of covalent
compounds include CS2 (carbon disulfide), PCl5 (phosphorus
pentachloride), and N2O4 (dinitrogen tetroxide).
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