Electronegativity and the Polar Covalent Bond

It is easy to see from the examples in the previous section how two identical atoms can share electrons to achieve an octet and form diatomic molecules. Because each of our examples dealt with identical atoms, the electrons can be considered to be shared equally by each atom. The bond formed when the atoms are equally shared can be thought of as a pure covalent bond. But what happens in covalent compounds Remember, a compound contains two different elements. When atoms of two different elements are held together by covalent bonds, there is an unequal sharing of the electrons. The sharing of electrons in a covalent bond may be compared to you and a friend sharing a flashlight while walking down a dark street. If you and your friend both held the 

The electron density is greater nearer the chlorine atom in the HCl molecule. Dots represent the nuclei. 

The point to emphasize with polar covalent bonds is that atoms do not equally share the bonding electrons. 

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