Chemical Nomenclature

Chemical nomenclature is the system of names that chemists use to identify compounds precisely. The systematic method of naming compounds is vital to the study of chemistry, because when a new substance is formulated, it must be named in order to distinguish it from all other substances.

Using this systematic method of naming compounds, the positive part is named and written first, followed by the negative part. The names and the elements are modified with suffixes and prefixes to identify the different types of compounds.

Atoms can combine to form compounds by losing, gaining, or sharing electrons. Chemists have discovered certain trends: it seems that elements tend to form ions with specific charges, or tend to form only a certain number of covalent bonds.

Naming Binary Ionic Compounds: In writing and naming a binary ionic compound such as NaCl, the metal comes first, and the nonmetal 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. For example, the metals in groups 1 and 2. and aluminum in group 3 always have only one oxidation number.

2. Binary compounds containing metals of variable oxidation number. There are two systems that are commonly used:

– First, the Stock method. Currently, it 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, copper (I) fluoride.

Second, 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. For example, cuprous fluoride.

Naming Binary Molecular Compounds: Binary molecular compounds are composed of two nonmetallic elements. For example, carbon and oxygen can form carbon monoxide (CO).

As in naming binary ionic compounds, the procedure is to write the least electronegative element first, using its English name. The more nonmetallic element is written second with -ide as a suffix (for example, silicon dioxide).

Since nonmetals usually have variable oxidation numbers, a Latin or Greek prefix (mono= 1, di= 2, tri = 3, tetra= 4, penta = 5, and so on) is attached to the name of each element to indicate the number of atoms of that element in the molecule (for example, carbon dioxide, CO₂).

Note: There are exceptions to this system. Some compounds are referred to by their common names. For example, the compound H₂O is  called water, and the compound NH₃ is called ammonia.