Empirical formula gives us the ratio between different atoms in a molecule. Molecular formula gives us the actual number of different atoms in a molecule. Molecular formula can be the same as empirical formula or can be a simple multiple of it. For example, in case of methane (represented as CH4), there are 4 atoms of hydrogen to every atom of carbon: the ratio of carbon atoms to hydrogen atoms is 4:1. This is its empirical formula and also the molecular formula. Compare that with butene (represented as C4H8), where 4 atoms of carbon are combined with 8 atoms of hydrogen. The molecular formula is C4H8, whereas the empirical formula is CH2, since the ratio of carbon atoms to hydrogen atoms is 1:2. In this case, empirical and molecular formula are different.
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