Based on atomicity, molecules can be classified as: •
Monoatomic (composed of one atom). Examples include He (
helium), Ne (
neon), Ar (
argon), and Kr (
krypton). All
noble gases are monoatomic. •
Diatomic (composed of two atoms). Examples include H2 (
hydrogen), N2 (
nitrogen), O2 (
oxygen), F2 (
fluorine), and Cl2 (
chlorine).
Halogens are usually diatomic. •
Triatomic (composed of three atoms). Examples include O3 (
ozone). • Tetratomic (composed of 4 atoms), Pentatomic (composed of 5 atoms), Hexatomic (composed of 6 atoms), Heptatomic (composed of 7 atoms), Octatomic (composed of 8 atoms) Atomicity may vary in different
allotropes of the same element. The exact atomicity of
metals, as well as some other
elements such as
carbon, cannot be determined because they consist of a large and indefinite number of atoms
bonded together. They are typically designated as having an atomicity of 2. The atomicity of
homonuclear molecule can be derived by dividing the
molecular weight by the
atomic weight. For example, the molecular weight of oxygen is 31.999, while its atomic weight is 15.879; therefore, its atomicity is approximately 2 (31.999/15.879 ≈ 2). == Examples ==