Ar(g)+e−⟶Ar− (g) (endothermic) H(g)+e−⟶H− (g) (exothermic) Na(g)⟶Na+(g)+e− (endothermic) O−(g)+e−⟶O2−(g) (endothermic) - Electron gaining enthalpy (EGE) of H(g ) is negative while that of Ar(g) is positive due to ns2np6 configuration. - Second EGE is always positive for an atom. - Ionization potential of an atom is positive.