Electronegativity is defined as the ability to attract a shared pair of electrons to itself is called electronegativity. The electronegativity of any given element is not constant, it changes from element to element to which it is bound. Though it is not a measurable quantity, it does provide a means predicting the nature of the force that holds a pair of electrons.

On the other hand, Electron gain enthalpy is defined as the amount of energy released when an electron is added to a gaseous isolated atom or ion. It a measurable quantity. The electron gain enthalpy of an atom measures the tightness with which it binds an additional electron to itself. The electron gain enthalpy is expressed in eV per atom or kJmol^-1

X(g) + e^-→ X^- (g) + Energy (Electron gain enthalpy)

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