GCSE Chemistry (AQA)

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Advanced Ionic Formulae

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Bonding, structure, and the properties of matter Chemical bonds, ionic, covalent and metallic

Advanced Ionic Formulae

3:37 Ionic Compounds and Formulae
Spec 4.1.1.1
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  • Some ions cannot be deduced using the periodic table and need to be memorized.
  • The hydroxide ion is an example, made up of oxygen and hydrogen with a single negative charge.
  • An ion made up of two or more elements is known as a compound ion.
  • Positive ions (cations) to memorize include:
  • Lead forms a Pb����� ion.
  • Silver forms an Ag��� ion.
  • Ammonium ion (NH������) is a compound ion.
  • Negative ions (anions) to memorize include:
  • Carbonate ion: CO��������
  • Hydroxide ion: OH���
  • Sulfate ion: SO��������
  • Nitrate ion: NO������
  • These compound ions must be memorized as their charges cannot be deduced from the periodic table.
  • Example: Chemical formula of barium hydroxide.
  • Step 1: Identify ions - Barium (Ba�����) and hydroxide (OH���).
  • Step 2: Balance charges - Need two OH��� ions to balance Ba�����.
  • Step 3: Write formula - Ba(OH)���, using brackets for multiple compound ions.
  • Swap and drop method can be used to determine formulas.
  • Example: Chemical formula of ammonium sulfate.
  • Step 1: Identify ions - Ammonium (NH������) and sulfate (SO��������).
  • Step 2: Use swap and drop method - Final formula is (NH���)���SO���, with brackets around NH��� for multiple ions.

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