There are two subtypes of covalent bonds. The H2 molecule is a good example of the first type of covalent bond the nonpolar bond. because both atoms in the H2 molecule have an equal attraction or affinity for electrons the two atom equally share the bonding electron and a nonpolar covalent bond is formed. Whenever two atoms of the same element bond together a nonpolar bond is formed.A polar covalent bond is formed when electrons are unequally shared between two atoms. Polar covalent bonding occurs because one atom has a stronger affinity for electrons than that of the other (yet not enought to pull the electrons away completely and form an ion). In a polar covalent bond the bonding electrons will spend a greater amount of time around the atom that has the stronger affinity for electrons. A good example of a polar covalent bond is the hydrogen - oxygen bond in the water molecule.

2H + 0 = H20

Water molecule contain two hydrogen atoms bonded to one oxygen atom. Oxygen with six valence electrons needs two additional electrons to complete its valence shell. Each hydrgen contains one electron. Thus oxygen shares the electrons from two hydrogen atoms to complete its own valence shell. and in return shares two of its own electrons with each hydrogen completing the H valence shells The primary difference between the H-O bond in water and the H-H bond is the degree of electron sharing. The loarge oxygen atom has a stronger affinity for electrons than the small hydrogen atoms. Becuase oxygen has a stronger pull on the bonding electrons this leads to unequal sharing and the formation of a polar covalent bond.