# Chemical Formulae

1. Each element is represented by its own chemical symbol.
2. In an element, the chemical formula represents the atoms in the molecule.
3. The chemical formula tells us:
1. the types of atoms or ions in the compound,
2. the number of atoms or ions in the compound,
4. For example, the chemical formula for ethene is C2H4. This shows that ethene is the result of the combination of the elements carbon and hydrogen, and there are 2 carbon atoms and 4 hydrogen atoms in each molecule of ethene.
5. Generally, chemical formula can be divided into
1. Empirical formula
2. Molecular formula
6. The empirical formula of a substance is the chemical formula that gives the simplest whole-number ratio of atoms of each element in the substance.
7. The molecular formula of a substance is the chemical formula that gives the actual number of atoms of each element in the substance.