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Naming Ionic Compounds

Key Concepts

  • Positively charged ions are called cations

  • Negatively charged ions are called anions

  • The cation is always named first.

Cations

Cations can be metals or polyatomic ions

  • The ammonium ion (NH4+) is an example of a polyatomic cation

  • Hydrogen can also form a cation, H+, in which case the name hydrogen is used in naming.

  • For metals that have only one possible charge (valency) the name of the metal is used.
    Examples are Group 1 (IA) metals (charge 1+), Group 2 (IIA) metals (charge 2+), Aluminium (charge 3+), Zinc (charge 2+), Silver (charge 1+)

  • For metals that can have more than one charge (valency) the name of the metal is succeeded by the valency in capital Roman numerals in brackets
    OR
    by using the suffix -ous for the lowest valency and -ic for the highest valency and sometimes with the Latinised name for the metal
Element Cation Preferred Name Other Name
copper Cu+ copper(I) cuprous
Cu2+ copper(II) cupric

iron Fe2+ iron(II) ferrous
Fe3+ iron(III) ferric

lead Pb2+ lead(II) plumbous
Pb4+ lead(IV) plumbic

mercury Hg22+ mercury(I) mercurous
Hg2+ mercury(II) mercuric

tin Sn2+ tin(II) stannous
Sn4+ tin(IV) stannic

Anions

Anions can be a negatively charged element or a polyatomic ion

  • Negatively charged elements have the suffix -ide
    Examples are oxide (O2-), sulfide (S2-), fluoride (F-), chloride (Cl-), bromide (Br-), iodide (I-), nitride (N3-), hydride (H-)

  • Polyatomic ions which include oxygen in the anion have the suffixes -ate or -ite. "ate" means there is more oxygen in the anion than one ending in "ite"

    Examples: sulfate (SO42-) has more oxygen than sulfite (SO32-), nitrate (NO3-) has more oxygen in the anion than nitrite (NO2-)

    Other examples are carbonate (CO32-), phosphate (PO43-) and permanganate (MnO4-)

    Exception: OH- is named hydroxide

Examples

Ionic Compounds containing ions of elements

  • MgO
    CATION: Mg2+ is named magnesium as magnesium belongs to Group 2 (IIA) and can only have one charge (valency)
    ANION: O2- is named oxide
    Name of compound is magnesium oxide

  • FeS
    CATION: Fe2+ is named iron(II) or ferrous as iron can have a charge of either 2+ or 3+
    ANION: S2- is named as sulfide
    Name of compound is iron(II) sulfide or ferrous sulfide

  • LiH
    CATION: Li+ is named as lithium since lithium is a Group 1 (IA) metal and can have only one charge (valency)
    ANION: H- is named as hydride
    Name of compund is lithium hydride

  • H2S
    CATION: H+ is named as hydrogen
    ANION: S2- is named as sulfide
    Name of compound is hydrogen sulfide

Ionic compounds containing polyatomic ions

  • NaOH
    CATION: Na+ is named as sodium (Group 1 metal)
    ANION: OH- is named as hydroxide
    Name of compound is sodium hydroxide

  • CaCO3
    CATION: Ca2+ is named as calcium (Group 2 metal)
    ANION: CO32- is named as carbonate
    Name of compound is calcium carbonate

  • FeSO4
    CATION: Fe2+ named as iron(II) or ferrous
    ANION: SO42- named as sulfate
    Name of compound is iron(II) sulfate or ferrous sulfate

  • FeSO3
    CATION: Fe2+ named as iron(II) or ferrous
    ANION: SO32- named as sulfite
    Name of compound is iron(II) sulfite or ferrous sulfite

  • (NH4)3PO4
    CATION: NH4+ named as ammonium
    ANION: PO43- named as phosphate
    Name of compound is ammonium phosphate


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