Introduction to Covalent Bonding: Bonding between non-metals consists of two electrons shared between two atoms. In covalent bonding, the two electrons shared by the atoms are attracted to the nucleus of both atoms. Neither atom completely loses or gains electrons as in ionic bonding. There are two types of covalent bonding: 1. Non-polar bonding with an equal sharing of electrons. 2. Polar bonding with an unequal sharing of electrons. The number of shared electrons depends on the number of electrons needed to complete the octet.

NON-POLAR BONDING results when two identical non-metals equally share electrons between them. One well known exception to the identical atom rule is the combination of carbon and hydrogen in all organic compounds.

IODINE: Iodine forms a diatomic non-polar covalent molecule. The graphic on the top left shows that iodine has 7 electrons in the outer shell. Since 8 electrons are needed for an octet, two iodine atoms EQUALLY share 2 electrons.

OXYGEN: Molecules of oxygen, present in about 20% concentration in air are also a covalent molecules . See the graphic on the left the Lewis symbols. There are 6 electrons in the outer shell, therefore, 2 electrons are needed to complete the octet. The two oxygen atoms share a total of four electrons in two separate bonds, called double bonds. The two oxygen atoms equally share the four electrons.