Introduction to Covalent Bonding:

Bonding between non-metals consists of two electrons shared between two atoms. Using the Wave Theory, the covalent bond involves an overlap of the electron clouds from each atom. The electrons are concentrated in the region between the 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.
 Comparison of Ionic, Polar and Non-Polar Bonding


The simplest non-polar covalent molecule is hydrogen. Each hydrogen atom has one electron and needs two to complete its first energy level. Since both hydrogen atoms are identical, neither atom will be able to dominate in the control of the electrons. The electrons are therefore shared equally. The hydrogen covalent bond can be represented in a variety of ways as shown on the right:

The "octet" for hydrogen is only 2 electrons since the nearest rare gas is He. The diatomic molecule is formed because individual hydrogen atoms containing only a single electron are unstable. Since both atoms are identical a complete transfer of electrons as in ionic bonding is impossible.

Instead the two hydrogen atoms SHARE both electrons equally.


Iodine forms a diatomic non-polar covalent molecule. The graphic 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;


Molecules of oxygen, present in about 20% concentration in air are also a covalent molecules . Click to see the graphic of 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.

Octet Rule: Elemental atoms generally lose, gain, or share electrons with other atoms
in order to achieve the same electron structure as the nearest rare gas with eight
electrons in the outer level.

The proper application of the Octet Rule provides valuable assistance in predicting and explaining various aspects of chemical formulas.