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Electronegativity

Electronegativity of an element is the tendency of an atom to attract the shared pair of electrons towards itself. It is a qualitative measure, because unlike ionization enthalpy and electron gain enthalpy which is related to atoms in the isolated gaseous state, it is in the bonded state and hence not a measurable quantity. Although a number of numerical scales of electronegativity such as Pauling scale, Mulliken-Jaffe scale, Allred Rochow scale have developed. Yet the Pauling scale is most widely used.

The electronegativity of any given element is not constant, it varies depending on the element to which it is bonded. Even though it is a qualitative quantity, it helps in the prediction of the type of bond which exists between two bonded atoms. The electronegative values of the elements increase along the period from left to right and decreases down the group. This is because as we move across the period from left to right, nuclear charge increases and atomic radius decreases whereas moving down the group atomic radius as well as screening effect increases. Consequently the nuclear attraction on the electrons increases across the period And decreases down the group. Fluorine has the highest tendency to attract the shared pair of electrons and cesium has a very low electronegative value i.e. tendency to attract the shared pair of electrons is very low.

On collecting all the evident factors regarding atomic radius, electronegativity, ionization enthalpy, electron gain enthalpy etc. , we find they all to be closely related to each other. For example, as the effective nucleus charge increases, the atomic radii decreases in a period and electronegativity increases. The ionization enthalpy and negative electron gain enthalpy also increase. This shows that the tendency to gain electrons is increasing that is non-metallic character increases and metallic character decreases from left to right in a period.

On the other hand, moving down the group the shielding effect increases. Thus reducing the nuclear force of attraction on electrons, consequently the atomic radius increases. The electronegativity decreases the ionization enthalpy and negative electron gain enthalpy values also decrease. This shows that the tendency is donate electrons increases i.e., metallic character increases and non-metallic character decreases.