CHEMISTRY - Polar and Non-Polar Covalent Bond

1. Non-polar Covalent Bonds - If two similar atoms come close to each other and form a bond by sharing their electrons, the shared electrons are equally attracted by the atoms as the electro negativity of the atoms is same. In other words, the shared electrons are not displaced towards any one atom. Hence, no poles are developed. This leads to the formation of completely non-polar bond. For example, if two hydrogen atoms form a bond, the electron pair will lie exactly in the middle between the two atoms and the resultant is non-polar. The important characteristics of a non-polar bond is that the electron cloud is completely systemic and there is no charge separation at all. 

2. Polar Covalent Bonds - When two dis- similar atoms, having different electro-negativities combine together to form a covalent bond, the shared pair of electrons does not lie at equal distances from the of both the bonded atoms but shifts towards the atom having greater electro negativity. Since the more electro negativity atom attracts the electrons more strongly, the distribution of electrons gets distorted, i.e. The electron cloud is displaced more towards the more electro negative atom. As a result, one end of the molecule Having more electro negative atom becomes slightly negatively charged whilethe other end acquires slightly positive charge. Thus, positive and negative roles are developed and this type of bond is called polar covalent bond. Lets consider the case of hydrogen chloride molecule. Chlorine is more electro negative than hydrogen. So the force of attraction, on the shared pair, exerted by chlorine is more than that by hydrogen. Hence, it will be shifted towards chlorine, i.e. Electron density of the electron cloud is more concentrated on chlorine side than on the hydrogen side. Molecules having polar bond are called polar molecules. In case of electro negativity difference between the two atoms bonded by a covalent bond is high, an electron can be completly free.