A chemical symbol is a one- or two-letter abbreviation used to represent a chemical element. For example, the chemical symbol for hydrogen is H, the chemical symbol for oxygen is O, and the chemical symbol for sodium is Na.

A chemical formula is a group of chemical symbols that represents a compound. A chemical formula indicates the elements that make up a compound and the relative proportions of those elements. For example, the chemical formula for water is H2O, which means that water is made up of two atoms of hydrogen and one atom of oxygen.