What Are Elements and Compounds?

The definitions of elements and compounds have changed very little in the past 200 years, but chemistry itself has changed a great deal over time. Any form of an element has been considered as the element itself and a compound had to have an exact atomic composition that included two or more different elements. This commentary suggests that only the atomic form of each element should be considered as the element and most other forms should be called elementary substances. A publication of the International Union of Pure and Applied Chemistry (IUPAC) has stated that compounds can be formed by a single element. The author agrees that in terms of modern chemical bonding both heteronuclear and homonuclear molecules can be considered as compounds.