Polar and non-polar covalent bonds. A covalent bond is formed by the mutual sharing of electrons between two atoms. If the two atoms are identical e.g. in H2, CI2 etc, the shred pair of electron is attracted equally by both the atoms and hence it remains exactly in the centre of the two atoms as shown below:

              H x H                                        CI x CI

Thus neither of the two atoms in such molecules acquires positive or negative charge. The bond thus formed between two identical toms is called no polar covalent bond. On the other hand, if the two atoms are dissimilar,e.g. in the HCI molecule, chlorine atom is more electronegative* than the H-atom. Hence the electron pair is more attracted towards the chlorine atom than towards the hydrogen atom. In other words, the shared pair of electrons is more displaced towards the chorine atom then towards hydrogen atom. As a result, the chorine end of the molecule acquires a slight negative charge  while the hydrogen end of the molecule acquires a slight positive charge . The bond thus formed between the two dissimilar atoms .(having slightly different electron nativities) is called a polar covalent bond and the molecule is called a dipole (because it ahs develoed+ve and –ve poles). Thus the situation in HCI may be represented as shown in fig.

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