1. Tendency to form negative ions, measured by combining ionization-potential and electron-affinity values for an element to find the degree to which its atoms attract electrons.
2. The ability of an atom to attract electrons, usually in non-metallic, acid-forming elements. Elements with sharply contrasting electronegativities tend to form ionic compounds (see ionic bond), e.g. NaCl, where Na and Cl have electronegativities of 0.9 and 3.0 respectively. Elements with similar electronegativities are likely to form covalent bonds, e.g. CH4 (methane), where C and H have electronegativities of 2.5 and 2.1 respectively. See valency.