Writing formulae is a difficult, but key part of a chemist's arsenal.

With two elements (not transition metals)[edit | edit source]

  • 1. Find which group the elements are in.
  • 2. Work out what the valency of the elements are (with groups 1-3, the valency is the group number; with groups 5-7, the valency is 8 minus the group number.
  • 3. With the two valencies, work out the integer ratio between them, for example with 2 and 3 the ratio is 3:2.

Example:

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