A chemical formula is a way to represent the composition of a chemical substance using symbols and numbers. It shows the types and quantities of atoms in a molecule. For example, the chemical formula for water is H2O, which indicates that each molecule contains two hydrogen atoms and one oxygen atom. Chemical formulas can be classified into two main types: empirical and molecular. The empirical formula gives the simplest whole-number ratio of atoms, while the molecular formula shows the actual number of atoms in a molecule. For instance, the molecular formula for glucose is C6H12O6, indicating it contains six carbon, twelve hydrogen, and six oxygen atoms.