What is the difference between molecular and empirical formulae?

The molecular formula shows the actual number of atoms of each element in a molecule, while the empirical formula shows the simplest ratio of these atoms.

The molecular formula of a compound provides information about the actual number of atoms of each element present in one molecule of the compound. For instance, the molecular formula of glucose is C6H12O6, which means one molecule of glucose contains 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. This formula gives a clear picture of the actual composition of the molecule.

On the other hand, the empirical formula of a compound represents the simplest whole number ratio of the atoms of each element in the compound. It does not necessarily provide the actual number of atoms in a molecule, but rather the simplest proportional numbers of atomic types. For example, the empirical formula of glucose is CH2O, which shows that in glucose, the ratio of carbon to hydrogen to oxygen is 1:2:1.

It's important to note that while the molecular formula of a compound can be the same as its empirical formula, this is not always the case. For instance, the molecular formula of water is H2O, which is also its empirical formula. However, for glucose, the molecular formula (C6H12O6) is different from its empirical formula (CH2O).

Understanding the difference between these two types of formulae is crucial in chemistry. The molecular formula provides a detailed view of the molecule's composition, which can help in understanding its properties and how it reacts with other substances. The empirical formula, while less detailed, provides a simplified view of the molecule's composition, which can be useful in identifying patterns and making comparisons between different compounds.