Homonuclear molecules, or
homonuclear species, are
molecules composed of only one type of
element. Homonuclear molecules may consist of various numbers of
atoms, depending on the element's properties. Some elements form molecules of more than one size.
Noble gases rarely form bonds, so they only have one atom. The most familiar homonuclear molecules are
diatomic, meaning they consist of two
atoms, though not all diatomic molecules are homonuclear. Homonuclear diatomic molecules include
hydrogen (H
2),
oxygen (O
2),
nitrogen (N
2) and all of the
halogens.
Ozone (O
3) is a common triatomic homonuclear molecule. Homonuclear tetratomic molecules include
arsenic (As
4) and
phosphorus (P
4).