Electronegativity of an element is the tendency of its atoms to attract the shared pair of electrons towards itself in a covalent bond.
The electronegativity of any given element depends upon the following factors:
1) State of hydridization
A sp-hybridized carbon is more electronegative than sp2 hybridised carbon, which in turn is more electronegative than a sp3 hybridised carbon.
2) Oxidation state of the element
As the oxidation state of the element increases, the electronegativity increases.
3) Nature of the substituents attached to the atom
The carbon atom in CF3I acquires greater positive charge than in CH3I .
The electronegativity values for the elements increases along a period from left to right and decreases down a group. As we move along the period from left to right nuclear charge increases and atomic radius decreases whereas when we move down the group ,atomic radius as well as cleaning effect increases.
Application of electronegativity
Metallic and non metallic character
As the electronegativity increases, the non metallic character increases. As the electronegativity decreases, the metallic character increases.
Fluorine with the highest electronegativity of 4 is the most non metallic element and caesium with the lowest electronegativity of 0.7 is the most metallic element.
Polar and non-polar bonds
A bond between two similar atoms is said to be known non-polar since the shared pair of electrons is equally attracted by the two atoms as the electronegativity of the atoms is the same.
For Ex: H2 , Cl2, O2, N2
The electronegativity of the two atoms forming a bond is different, the shared pair of electrons is attracted more towards the more electronegative element atom.The more electronegative atom acquires a partial negative charge and the less electronegative atoms acquire a partial positive charge. As a result ,two poles are developed and the molecule is said to be Polar.
For Ex: H-F , HCl, HBr, HI
Higher the difference in electronegativity of the two binding atoms, the more is the dipole moment of the molecule.
A polar covalent bond is said to possess some partial ionic character. If the electronegativity difference between the two atoms is 1.9 ,the bond is said to have 50% ionic and 50%covalent character and it is difference increases the ionic character for the increases.