Saturday, May 14, 2011

Polar and Non Polar Covalent Bond

In the H2 or Cl2molecule, the two electrons constituting the covalent bond are equally shared by the two identical nuclei. Due to even distribution of electrons between the two nuclei, the molecule remains neutral. Such a bond is called Non-Polar Covalent Bond. However, when two different atoms are joined by a covalent bond as in HCl, the electron pair is not shared equally.
Due to a greater attraction of one nucleus (Cl) for the electrons, the shared pair is displaced towards it. This makes one end of the bond partially positive (δ+) and the other partially negative (δ).
    A covalent bond in which electrons are shared unequally and the bonded atoms acquire a partial positive and negative charge, is called a Polar Covalent Bond.
    A molecule having partial positive and negative charge separated by a distance is commonly referred to as a dipole
(two poles). The dipole of a bond is indicated by an arrow from positive to negative end with a crossed tail as shown above in HCL molecule.
    Since two atoms of different atoms do not have exactly the same attraction for electrons in a bond, all bonds between unlike atoms are polar to some extent. The amount of polarity of a bond is determined by the difference of electro negativity (or tendency to attract electrons) of the two bonded atoms. The greater the difference of electro negativity between two atoms, greater the polarity. As a matter of fact, if this difference is around 1.9 & 2.9, the bond is generally ionic, meaning there by, that one atom has gained complete control of electron pair in the bond.

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