Naming Compounds and Writing Formulas
There are fundamentally two different kinds of compounds:
ionic and covalent (molecular).
Ionic Compounds:
Ionic compounds are formed between positive ions (cations)
and negative ions (anions). The positive ions are almost always
formed from a metal element, with one exception, NH4+ (ammonium
ion). The negative ion may be formed from one nonmetal element,
or the negative ion may contain two or more elements (polyatomic
ion). Ionic compounds are held together by the force of
electrostatic attraction between the positive ions and the
negative ions.
Covalent (molecular) Compounds
Covalent compounds usually contain only nonmetals, and the
atoms are held together by the sharing of electrons. A
collection of atoms thus held together is called a molecule.
(The atoms in polyatomic ions are also held together by the
sharing of electrons, but such ions may include metals.)
NOMENCLATURE OF BINARY COMPOUNDS
A binary compound is a compound that contains only two
elements. If one is a metal and the other a nonmetal, then the
compound is an ionic compound. If both are nonmetals, then the
compound is a covalent compound.
I.
Nomenclature of ionic BINARY compounds.
A.
Naming.
ion.
The metal ion is named first, then the nonmetal
IF the metal can form only one kind of ion, then the ion has
the same name as the metal. If the metal can form two different
ions, there are two ways of naming the metal ion: the common
naming system and the Stock naming system.
The metals in the first two columns of the periodic table
(Groups 1A and 2A) form only one kind of ion. (Note: Hydrogen is
a nonmetal which can form an H+ ion or an H- ion.) Group 1 metals
form 1+ ions and group 2 metals form 2+ ions. This gives these
metal ions the stable electron configuration of the preceding
noble gas.
The nonmetal ion is named second. The nonmetal elements
form only one kind of ion. The name of the nonmetal ion is
obtained by changing the ending of the element name to “-ide”.
(Examples: the ion formed from oxygen is the oxide ion; the ion
formed from fluorine is the fluoride ion.) In order to form
ions, the nonmetals add electrons until they have the electron
configuration of the next noble gas. Thus group 5A nonmetals
form 3- ions, group 6A nonmetals form 2- ions, and group 7A
nonmetals (the halogens) form 1- ions. When hydrogen is the
nonmetal and forms the ion H-, it takes the name “hydride”.
The metal ions which we will study which have two possible
charges are
Ion
Common Name
Stock Name
Fe2+
Fe3+
ferrous
ferric
iron (II)
iron (III)
Cu+
Cu2+
cuprous
cupric
copper (I)
copper (II)
Sn2+
Sn4+
stannous
stannic
tin (II)
tin (IV)
Au+
Au3+
aurous
auric
gold (I)
gold (III)
Hg22+
mercurous
Hg2+
mercuric
mercury (I) Note that this ion
consists of 2 Hg+ ions
mercury (II)
Pb2+
Pb4+
plumbous
plumbic
lead (II)
lead (IV)
Note two other metals that form only one kind of ion:
silver (Ag+) and zinc (Zn2+)
B.
Writing Formulas from Names - Binary Ionic Compounds
From the name, identify both the positive and negative ions,
including their charges. Then combine the positive and negative
ions so that total positive charge = total negative charge.
C.
Writing Names from Formulas - Binary Ionic Compounds
Start by identifying THE NEGATIVE ION, both as to name and
charge. From this, identify the charge on the positive ion
(remember: total positive charge = total negative charge).
Then, identify the positive ion by name. Name the positive ion
first, then the negative ion.
II.
Nomenclature of covalent BINARY compounds, including naming
of binary acids.
Covalent binary compounds consist of two nonmetal elements.
The compounds are named using prefixes that indicate the number
of atoms of each element: mono-, di-, tri-, tetra- (or tetr-),
penta- (or pent-), hexa- (or hex-), hepta- (or hept-). If only
one atom of the first-named element is present, then the monoprefix is not used for the first-named element.
Examples:
SO2
sulfur dioxide
N2O4 dinitrogen tetroxide
P2O5
diphosphorous pentoxide
NOTE: Compounds in which hydrogen is the first-named element do
NOT use prefixes in the naming. When hydrogen is the first-named
element, it can be treated as having a 1+ charge; the naming is
really more like that for binary ionic compounds:
Examples:
HF
HCl
HBr
HI
hydrogen
hydrogen
hydrogen
hydrogen
H2S
hydrogen sulfide
H2Se
fluoride
chloride
bromide
iodide
hydrogen selenide
These compounds are generally gases, and this would be indicated
as, for example, HF(g).
When these compounds are dissolved in water, they form binary
acids. (NOTE: all acids have H as the first-named element.)
The notation (aq) indicates a compound that is dissolved in water
and is always used with acids. The names of these binary acids
begin with “hydro” and end with the name of the second-named
element (with its ending changed to “ic”), then the word “acid”:
HF(aq)
HCl(aq)
HBr(aq)
HI(aq)
hydrofluoric acid
hydrochloric acid
hydrobromic acid
hydroiodic acid
H2S(aq)
hydrosulfuric acid
H2Se(aq)
hydroselenic acid
NOMENCLATURE OF COMPOUNDS OTHER THAN BINARY COMPOUNDS
I.
Nomenclature of ionic compounds. The positive ion will be
either a positive metal ion or the NH4+ (ammonium) ion. The
negative ion will be a polyatomic ion, usually (but not always)
containing oxygen. (See table 5.7 on page 180 of the text.)
A.
Naming of ionic compounds.
1) The naming of the metal ions is the same as it is in the
case of binary compounds.
2) The name of each negative polyatomic ion must simply be
learned, along with the formula and charge. (See table 5.7 on
page 180 of the text.) However, in a series of negative ions
that differ only in the number of oxygen atoms they contain, a
pattern can be observed. (In these ions, the oxygen atoms are
combined with one other nonmetal atom; such ions are called
oxyanions. The name of the ion is based on the atom other than
oxygen, and the ending indicates the relative number of oxygen
atoms.)
a) If there are two ions in the series, the one with the
greater number of oxygen atoms ends in “ate” and the one with the
lesser number of oxygen atoms ends in “ite”. Examples are:
SO42- sulfate
NO3-
nitrate
PO43-
phosphate
SO32-
sulfite
NO2-
nitrite
PO33-
phosphite
b) If there are more than two members in the series, then
prefixes are needed in some cases; the following series will
illustrate:
ClOClO2ClO3ClO4-
hypochlorite
chlorite
chlorate
perchlorate
(Note: the halogens Br and I will each form a similar series.
For example, IO4- is periodate; IO- is hypoiodite; BrO2- is
bromite; BrO3- is bromate, etc.)
B.
Writing Formulas from Names
From the name, identify both the positive and negative ions,
including their charges. Then combine the positive and negative
ions so that total positive charge = total negative charge. If
more than one of a particular polyatomic ion is required in a
formula, then that polyatomic ion must be place in parentheses,
with the formula subscript outside of the parentheses.
Examples:
C.
calcium phosphate
Ca3(PO4)2
ammonium phosphite
(NH4)3PO3
Writing Names from Formulas
Start by identifying THE NEGATIVE ION, both as to name and
charge. From this, identify the charge on the positive ion
(remember: total positive charge = total negative charge).
Then, identify the positive ion by name. Name the positive ion
first, then the negative ion.
II.
Nomenclature of Oxyacids.
Oxyacids are acids containing hydrogen combined with an
oxyanion. Each hydrogen is taken to have a charge of 1+.
The name of an oxyacid is related to the name of the
corresponding oxyanion. The following series will illustrate:
ClOClO2ClO3-
hypochlorite
chlorite
chlorate
HClO(aq) hypocholrous acid
HClO2(aq) chlorous acid
HClO3(aq) chloric acid
ClO4-
perchlorate
HClO4(aq)
perchloric acid
More examples:
SO42- sulfate
SO32- sulfite
PO43PO33NO3NO2-
phosphate
phosphite
nitrate
nitrite
H2SO4(aq)
H2SO3(aq)
sulfuric acid
sulfurous acid
H3PO4(aq)
H3PO3(aq)
HNO3(aq)
HNO2(aq)
phosphoric acid
phosphorous acid
nitric acid
nitrous acid
Note: Many of the oxyacid formulas represent only the acid; for
example, no compound with the formula H2SO4 can be isolated
outside of water.