Electronegativity is the tendency of an atom in a chemical compound to attract the shared pair of electrons in a covalent bond toward itself. It is a relative, dimensionless quantity that reflects how strongly an atom pulls electrons in a bonding situation. Electron gain enthalpy, on the other hand, is the energy change that occurs when an isolated gaseous atom accepts an extra electron to form a negative ion. It is typically expressed in kJ/mol and represents how much energy is released (usually) or absorbed when an electron is added. The key differences are that electronegativity refers to the behavior of an atom within a molecule attracting bonded electrons, whereas electron gain enthalpy pertains to an isolated atom gaining an electron. Electronegativity is a qualitative measure of attraction in a bond, while electron gain enthalpy is a quantitative thermodynamic measure of electron acceptance by a free atom.