Naming Compounds – Chemistry 177

Covalent (Molecular) Compounds

  1. The first element in the compound is named first. (e.g., in H2O, Hydrogen is named first, Oxygen second)
  2. The second element in the compound is given an –ide ending
  3. Both elements are given prefixes determined by the number of each element in the compound. If there is only one of the first element, it is not given a prefix.

  • 1 — mono
  • 2 — di
  • 3 — tri
  • 4 — tetra
  • 5 — penta
/
  • 6 — hexa
  • 7 — hepta
  • 8 — octa
  • 9 — nona
  • 10 — deca
/ Examples using prefixes:
  • CCl4 — carbon tetrachloride
  • P2O5 — diphosphoruspentoxide
  • N2O — dinitrogen monoxide
  • ICl3 — iodine trichloride

Ionic Compounds

  1. The cation is always named first, the anion second.
  2. Cations are named for their element – e.g. the Na+ cation is simply called “sodium”
  3. Cations of transition metals and metals in groups IIIA-VIA must have the charge shown using roman numerals in parentheses after the cation name. Zinc, Cadmium, and Silver are the only three transition metals which have only one charge, and thus do not need to have their charge shown.
  4. The anion is named by adding –ide to the end of the element name if it is a single element anion.
  5. Oxyanions have special naming rules. As the number of oxygen attached to an element increases, the prefixes and suffixes change. The table below lists the prefixes used for naming oxyanions. Note – the “______ate” suffix does not always mean that there are 3 O atoms attached to the element! It is simply the suffix used for the most common oxyanion of that element (NO3 and SO4 are nitrate and sulfate, respectively). You just have to memorize which is the “-ate” oxyanion, and then remember the rules for increasing and decreasing the number of oxygen atoms.

Less oxygens

More oxygens / Hypo______ite
______ite
______ate
Per______ate / Example:
hypochlorite (HClO-)
Chlorite (HClO2-)
Chlorate (HClO3-)
Perchlorate (HClO4-)

Naming Acids

  1. Acids formed with a H+ ion and a single element anion are named by adding the prefix –hydro to the element named with a suffix of –ic and the word acid. E.g. HCl is hydrochloric acid, H2S is hydrosulfuric acid.
  2. The name of acids formed by H+ and a compound anion is formed using the name of the anion. If the anion is an oxyanion, the name transforms as follows:

Per____ate per____ic acid
____ate  ____ic acid
____ite ____ous acid
Hypo_____ite hypo____ous acid / Perchlorate (ClO4-) Perchloric acid (HClO4)
Sulfate (SO42-)  sulfuric acid (H2SO4)
Nitrite (NO2-)  nitrous acid (HNO2)
Hypobromite (BrO-) hypobromous acid (HBrO)