Naming Ionic Compounds

Key Concepts

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
copper	Cu²⁺	copper (II)	cupric

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

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

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

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

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

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

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