Effects of Exchange Energy and Spin-Orbit Coupling on Bond Energies

摘要

Since chemical reactions involve the breaking and making of bonds,understanding the relative strengths of bonds is of paramount importance in the study,teaching,and practice of chemistry.In a gaseous molecular substance ABW,the mean bond energy Z)A_B is equal to A//° for the atomization:AB_n(g)->A(g)+nB(g)divided by n.These quantities are frequently tabulated and invoked in undergraduate texts.Explanations of their periodicity-important in descriptive inorganic chemistry-are usually based on considerations of atomic size and bond polarity;bond energies tend to decrease with increasing bond length,and increase with increasing polarity.Implicit in the latter factor is eq 1,proposed by Pauling and used to construct the first scale of electronegativity (1).