Nomenclature for Ionic Compounds

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Ionic compounds consist of cations (positive ions) and anions (negative ions). The nomenclature, or naming, of ionic compounds is based on the names of the component ions. Here are the principal naming conventions for ionic compounds, along with examples to show how they are used:

• Roman Numerals
  A Roman numeral in parentheses, followed by the name of the element, is used for elements that can form more than one positive ion. This is usually seen with metals. You can use a chart to see the possible valences for the elements.

  Fe²⁺ Iron (II)
  Fe³⁺ Iron (III)
  Cu⁺ Copper (I)
  Cu²⁺ Copper (II)
  

• -ous and -ic
  Although Roman numerals are used to denote the ionic charge of cations, it is still common to see and use the endings -ous or -ic. These endings are added to the Latin name of the element (e.g., stannous/stannic for tin) to represent the ions with lesser or greater charge, respectively. The Roman numeral naming convention has wider appeal because many ions have more than two valences.

  Fe²⁺ Ferrous
  Fe³⁺ Ferric
  Cu⁺ Cuprous
  Cu²⁺ Cupric
  

• -ide
  The -ide ending is added to the name of a monoatomic ion of an element.

  H^- Hydride
  F^- Fluoride
  O^2- Oxide
  S^2- Sulfide
  N^3- Nitride
  P^3- Phosphide
  

• -ite and -ate
  Some polyatomic anions contain oxygen. These anions are called oxyanions. When an element forms two oxyanions, the one with less oxygen is given a name ending in -ite and the one with more oxgyen is given a name that ends in -ate.

  NO₂^- Nitrite
  NO₃^- Nitrate
  SO₃^2- Sulfite
  SO₄^2- Sulfate
  

• hypo- and per-
  In the case where there is a series of four oxyanions, the hypo- and per- prefixes are used in conjunction with the -ite and -ate suffixes. The hypo- and per- prefixes indicate less oxygen and more oxygen, respectively.

  ClO^- Hypochlorite
  ClO₂^- Chlorite
  ClO₃^- Chlorate
  ClO₄^- Perchlorate
  

• bi- and di- hydrogen
  Polyatomic anions sometimes gain one or more H⁺ ions to form anions of a lower charge. These ions are named by adding the word hydrogen or dihydrogen in front of the name of the anion. It is still common to see and use the older naming convention in which the prefix bi- is used to indicate the addition of a single hydrogen ion.

  HCO₃^- Hydrogen carbonate or bicarbonate
  HSO₄^- Hydrogen sulfate or bisulfate
  H₂PO₄^- Dihydrogen phosphate