Homonuclear molecules
Homonuclear molecules are formed from only one element. That is why known as homonuclear. These molecules can consist of various numbers of elements which depends on the properties of the element. Some of the elements form molecules of more than one size. Nobel gases have only one atom so they rarely form bond. Mostly homonuclear molecules are diatomic that is they have two atoms. Homonuclear diatomic molecules include: hydrogen (H2), oxygen (O2), nitrogen (N 2) and all of the halogens.
Heteronuclear Molecules:
Hetero-nuclear molecules are formed from more than one element. The motion of a single electron in the molecular orbitals is described in a molecule containing two unequal nuclear charges will not exhibit the g and u symmetry properties of the homonuclear diatomic case. The orbitals may still be classified as s, p, d, etc. because the molecular axis is still an axis of symmetry. Examples of Heteronuclear diatomic molecule are: Carbon Monoxide molecule, Hydrogen fluoride molecule.