The atomic symbol for each chemical element in a substance is shown in the substance's chemical formula.

Chemical formulas for elementary substances

An elementary substance is represented by a chemical formula that contains only one atomic symbol.

The atomic symbol in a chemical formula may be followed by a small number written lower than the symbol. This number is called a subscript. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript shows how many atoms are in each molecule.

For example, the chemical formula for the elementary substance oxygen, O₂, has a subscript of 2. This subscript shows that the atomic symbol O represents two atoms. The elementary substance O₂ and the chemical element represented by the atomic symbol O are both named oxygen. So, the formula tells you that each molecule of O₂ contains two oxygen atoms.

Chemical formulas for compounds

A compound is represented by a chemical formula that contains multiple atomic symbols.

The chemical elements in a compound are bonded together in a fixed ratio. This ratio is shown in a compound's chemical formula.

For example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. So, the ratio of beryllium atoms to fluorine atoms is 1 to 2. This ratio is shown in the chemical formula for beryllium fluoride, BeF₂. There is no subscript following the atomic symbol Be because that symbol represents one atom. The subscript 2 follows the atomic symbol F to show that the symbol represents two atoms.

There are more than 100 different chemical elements, or types of atoms. Chemical elements make up all of the substances around you.A substance may be composed of one chemical element or multiple chemical elements.

Substances that are composed of only one chemical element are elementary substances.

Substances that are composed of multiple chemical elements bonded together are compounds.

Every chemical element is represented by its own atomic symbol. An atomic symbol may consist of one capital letter, or it may consist of a capital letter followed by a lowercase letter. For example, the atomic symbol for the chemical element fluorine is F, and the atomic symbol for the chemical element beryllium is Be.