# What is the molecular formula of a compound?

The $\text{molecular formula}$ is what the name says on the tin.....
It expresses the proportions and identities of atoms in a discrete molecule, i.e. $\text{butane}$, ${C}_{4} {H}_{10}$, $\text{ethylene}$, ${C}_{2} {H}_{4}$, and this formula is used to determine the molecular mass (this is the distinction between $\text{molecular formula}$ and $\text{empirical formula}$, where the latter is the simplest whole number ratio defining constituent atoms in a species, and the former is a whole number multiple of the $\text{empirical formula}$ (and of course the multiple might be one).