electronegativity

electronegativity , in chemistry, tendency for an atom to attract a pair of electrons that it shares with another atom (see chemical bond ). For example, the molecule hydrogen chloride, HCl, consists of a hydrogen atom, H, and a chlorine atom, Cl, sharing a pair of electrons. If the pair of electrons are not shared equally, i.e., if they spend more time with one atom than with the other, the favored atom is said to be more electronegative. In the case of HCl, measurements indicate that the molecule has a dipole moment, that is, the chlorine end is relatively negative and the hydrogen end is relatively positive. This means that the electron pair spends more time with the chlorine atom than with the hydrogen atom and thus chlorine is more electronegative than hydrogen. Nonmetals have much higher electronegativities than metals; of the nonmetals, fluorine is the most electronegative, followed by oxygen, nitrogen, and chlorine. The larger the difference in electronegativity between two atoms, the more polar the bond between them. In the extreme case of a bond between a metal and a nonmetal, a complete transfer of electrons takes place.

electronegativity
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.

electronegativity
1. The 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 constrasting electronegativities tend to form ionic compounds (i.e. with ionic bonds), 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).