Types of Formulae

Confused by the types of formulae you are asked to learn about at AS level? 

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Empirical Formulae

The simplest whole number ratio of elements in a compound. For example, all alkenes have the empirical formula CH₂. 

The molecular formula for ethene (C₂H₄) and propene (C₃H₆) can be simplified to CH₂.

Molecular Formula

Gives the actual number of each kind of atom present. For example C₄H₁₀O is the molecular formula of the alcohol butanol with 4 carbon atom, 10 hydrogen atoms and 1 oxygen atom.

General Formulae

Represents any member of an homologous series. For example, the alkane with n carbons has the formula C_nH_2n+2.