NOMENCLATURE
Nomenclature can be defined as the terminology of chemical compounds. It represents the basic
"language of chemistry" and, just as the student who is studying French or Spanish must learn the
terminology of those languages, so must the chemistry student learn the basic terminology of the
discipline.
Life certainly becomes a bit easier, and safer for everyone around, if chemistry students are able to read
the formulas on the bottles of stock solutions correctly when they have only the names of these
substances on their lab sheet or vice versa.
Okay, so it's a given......one of the basic, most important tasks that a chemistry student needs to master
early on is that of Naming Compounds and Writing Formulas. There are several things that a student can
do to make these tasks less tedious.
Learn the correct symbols for the elements. (This is similar to reciting the alphabet...a, b, c..., as well as
identifying the symbols we use for each letter.)
Learn the names and formulas of seven (7) acids and ammonia. The acids and their formulas, along with
ammonia and its formula are:
hydrochloric acid
HCl
nitric acid
HNO3
acetic acid
HC2H3O2
perchloric acid HClO4
carbonic acid
H2CO3
sulfuric acid
H2SO4
phosphoric acid H3PO4
ammonia
NH3
Learn the meaning of several important prefixes and suffixes as they relate to the formulas of
polyatomic ions, cation charges, and anions.
Prefix/Sufix
Meaning
Example(s)
-ate
denotes the most common number of oxygen atoms
-ite
one less oxygen than in the "-ate" ion
per-
(1) one more oxygen than in the "-ate" ion, also
sulfate, nitrate, chlorate
sulfite, nitrite, chlorite
(2) one more oxygen than the most common number
(1) perchlorate, permanganate
(2) peroxide
hypo- one less oxygen than in the "-ite" ion
hypochlorite
ide-
ion contains only the atoms whose names are heard
hydroxide, chloride, sulfide nitride
-ic
(1) ending for acid that contains the "-ate" form of the ion
(2) indicates the higher oxidation number of some cations (older method, but still used)
(1) sulfuric, nitric, chloric
(2) ferric is iron in the 3+ state, cupric is copper in the 2+ state
-ous
(1) ending for acid that contains the "-ite" form of the ion
(2) indicates the lower oxidation number of some cations (also older method, but still used)
sulfurous, nitrous, chlorous
(1)
(2) ferrous is iron in the 2+ state, cuprous is copper in the 1+ state
hydro- -ic
hydrosulfuric
prefix and suffix used with acids whose anions contain no oxygen
hydrochloric,
Notice that the acids suggested for memorization, other than hydrochloric, all end in -ic, and thus
contain the -ate form of the polyatomic ion. You can therefore, quickly identify these ions when you see
them in the formula for some other compound or easily write the formula for a compound that contains
one of these ions. You can then use the meanings for the other prefixes and suffixes to expand your
repetoire of ions without having to memorize each of them separately.
Learn the names of the prefixes that are used to denote one (1) through ten (10) atoms in a formula.
1 = mono-
2 = di- 3 = tri- 4 = tetra-
5 = penta-
6 = hexa-
7 = hepta-
9 = nona-
8 = octa-
10 = deca-
Applying These Rules
There are two kinds of compounds for which students in high school and general chemistry are usually
expected to write formulas or to name. They are ionic compounds and binary covalent compounds. A
third kind that are also helpful to learn are those of the coordination compounds, but they have their
own set of rules for naming or writing and will not be covered here.
Writing Formulas
(Notes from: http://www.files.chem.vt.edu/RVGS/ACT/notes/Nomenclature.html)
Covalent Compounds: Nm – Nm (number name it)
Eg. CO2 It’s an Nm-Nm (look at periodic table) so: Carbon dioxide
Never number name first element in the compound on number name the ones that follow the first
Ionic compounds : M-Nm ( just name it)
Eg. NaCl Its M-Nm ( look at periodic table) so : Sodium chloride