Naming Covalent Compounds

Naming Binary Covalent Compounds

When a pair of elements form more than one type of covalent compound, Greek prefixes are used to indicate how many of each element are in a compound. For example:

N2Odinitrogen monoxide
NOnitrogen monoxide
N2O3dinitrogen trioxide
N2O5dinitrogen pentoxide

Some of the Greek prefixes are given in the table below:

PrefixNumber of Particular Element

Rules for Binary Covalent Compounds

  1. The prefix mono is never used for naming the first element of a compound.
  2. The final o or a of a prefix is often dropped when the element begins with a vowel.

For example, for CO the name will be carbon monoxide, and the final o of mono is dropped. Remember, it's only the final o or a. So, the name of ClO2 will be chlorine dioxide, and no vowels are dropped.

How do you know which element goes first? The element that comes first in the following list "goes" first.

B, Si, C, Sb, As, P, N, H, Te, Se, S, I, Br, Cl, O, F

Finally, H2O, which according to the rules should be called dihydrogen monoxide is always called water, and NH3, or nitrogen trihydride, is always called ammonia.

Naming Acids, Oxyacids and Their Salts

  1. If the anion does not contain oxygen, then the acid is named with the prefix hydro- and the suffix -ic.
    • For example, when gaseous HCl is dissolved in H2O, it forms hydrochloric acid.
    • HCN in H2O is hydrocyanic acid.

    Before we learn the rule for naming oxyacids, let's learn the rules for naming oxyanions. What are oxyanions? They are anions formed from oxygen and a nonmetal. Here are some examples: ClO4-, ClO3-, ClO2-, ClO-, SO42-, SO32-.

    There are two rules for naming these:

  2. If there are only two members in the same series, then the anion with the least number of oxygens ends in -ite, and the anion with the most ends in -ate.
    • For example, SO32- is sulfite and SO42- is sulfate.
  3. When there are more than two oxyanions in a series, hypo- (less than) and per- (more than) are used as prefixes. Here are some examples:
    • ClO- is hypochlorite
    • ClO2- is chlorite
    • ClO3- is chlorate
    • ClO4- is perchlorate
    Finally, here are the rules for naming acids of oxyanions.
  4. If the anion name ends in -ate, then the acid name ends in -ic or -ric.
  5. If the anion name ends in -ite, then the acid name ends in -ous.

Here are examples of the last three rules:

AcidAnionAcid Name
HClOhypochloritehypochlorous acid
HClO2chloritechlorous acid
HClO3chloratechloric acid
HClO4perchlorateperchloric acid

Homework from Chemisty, The Central Science, 10th Ed.

2.57, 2.59, 2.61, 2.63, 2.65, 2.67