Names & Formulae of Ionic Compounds (Edexcel GCSE Chemistry)

Naming Ionic Compounds

• Ionic compounds contain metal and non-metal elements joined together as particles called ions

• The metal element’s symbol is always written first

• The non-metal element always takes on the name ending ‘– ide’ unless oxygen is also present,

  • For example, PbS is called lead sulfide and MgCl₂ is called magnesium chloride

• When oxygen is present the name ending is usually ‘-ate’

  • For example, CuSO₄ is copper sulfate, KClO₃ is potassium chlorate and Na₂CO₃ is sodium carbonate

Deducing Formulae

• The formulae of simple ionic compounds can be calculated if you know the charge on the ions

• Below are some common ions and their charges:

Common Ions & Their Charges Table

• For ionic compounds you have to balance the charge of each part by multiplying each ion until the sum of the charges = 0

• Example: what is the formula of aluminium sulfate?

  • Write out the formulae of each ion, including their charges

  • Al³⁺ SO₄^2-

• Balance the charges by multiplying them out:

  Al³⁺ x 2 = +6 and SO₄^2- x 3 = -6; so +6 – 6 = 0

• So the formula is Al₂(SO₄)₃