Compound Nomenclature

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 I metals (charge 1+), Group II 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 (O^2-), sulfide (S^2-), fluoride (F^-), chloride (Cl^-), bromide (Br^-), iodide (I^-), nitride (N^3-), 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 (SO₄^2-) has more oxygen than sulfite (SO₃^2-), nitrate (NO₃^-) has more oxygen in the anion than nitrite (NO₂^-)
  Other examples are carbonate (CO₃^2-), phosphate (PO₄^3-) 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 (II) and can only have one charge (valency)
  ANION: O^2- 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: S^2- 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 I 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: S^2- is named as sulfide
  Name of compound is hydrogen sulfide

Ionic compounds containing polyatomic ions

• NaOH
  CATION: Na⁺ is named as sodium (Group I metal)
  ANION: OH^- is named as hydroxide
  Name of compound is sodium hydroxide
• CaCO₃
  CATION: Ca²⁺ is named as calcium (Group II metal)
  ANION: CO₃^2- is named as carbonate
  Name of compound is calcium carbonate
• FeSO₄
  CATION: Fe²⁺ named as iron (II) or ferrous
  ANION: SO₄^2- named as sulfate
  Name of compound is iron (II) sulfate or ferrous sulfate
• FeSO₃
  CATION: Fe²⁺ named as iron (II) or ferrous
  ANION: SO₃^2- named as sulfite
  Name of compound is iron (II) sulfite or ferrous sulfite
• (NH₄)₃PO₄
  CATION: NH₄⁺ named as ammonium
  ANION: PO₄^3- named as phosphate
  Name of compound is ammonium phosphate