**Empirical formulae** – simplest whole number ratio of atoms in a compound

**Molecular formulae** – the exact nu,her of atoms in a molecule (the formula)

When creating formulae, remember to always use subscript numbers!

Calculating Empirical formulae –

- Divide by mass number
- Divide by smallest number
- Work out ratio
- Write empirical formula

Worked example: Iron Oxide –

- Iron = 2.24g / 56 (RFM) = 0.04
- Oxygen = 0.96g / 16 (RFM) = 0.06
- Divide both number products by 0.04, as it is the smallest number.
- The outcome of Oxygen, 0.06 / 0.04 = 1.5, you must multiply this to become a whole number – 3
- You must do the same to Iron, 1 x = 2
- Write empirical formula = Fe2O3

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