The empirical formula for magnesium oxide is MgO. This formula indicates that there are equal numbers of magnesium atoms and oxygen atoms in a molecule of magnesium oxide.
Chemical formulas are a shorthand way of describing the atomic makeup of a compound. There are two types of chemical formulas:
- Empirical — expresses the simplest ratio between the atoms in a compound
- Molecular — expresses the actual number of each atom in the smallest unit of the compound
It is possible for two or more compounds to have the same empirical formula but different molecular formulas. For example, the empirical formula for both butene and ethylene is CH2. However, a butene molecule actually contains four atoms of carbon and eight atoms of hydrogen. Its molecular formula is C4H8. Ethylene contains two atoms of carbon and four atoms of hydrogen per molecule, and its molecular formula is C2H4.