The chemical formula of a compound describes the composition of the molecules of the compound in terms of the symbols of elements and the number of atoms of each element present in one molecule of the compound. In the chemical formula of a compound, the elements present are denoted by their symbols and the number of atoms of each element are shown by writing their number as subscripts to the symbols of the respective elements.

Formula of a compound- Water-H20

Formula of an element-Sodium- Na.