Electronegativity is defined as the tendency of an element to attract the shared pair of electrons towards itself in a covalent bond. There is no specific unit for electronegativity. Electron gain enthalpy is the energy released when one mole of electron are added to gaseous atoms of an element. It can be negative or positive depending upon whether the electron is added or removed. An element has a constant value of the electron gain enthalpy that can be measured experimentally.