Valency and Molecular Structure

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THE connexion between the numerical valency exhibited by an atom and the number of its outside electrons, which prevailed in certain pre-wave mechanical theories of valency and in the theory of Heitler and London, appears to us of fundamental importance to the problem. It cannot be fortuitous that iodine, for example, which possesses two s- and five s-electrons, exhibits odd covalencies of 1, 3, 5 and 7. Nevertheless, this relationship appears to have been lost sight of in the chemical theories of Lowry, Sidgwick, and others on account of the con ception of co-ordinate covalency, in which only electrons belonging to one of the atoms concerned are made responsible for chemical combination. This conception appears to connect these theories with the theory of molecular orbitals (Herzberg, Lennard-Jones, Mulliken) in that chemical linkage is ascribed to the bonding power of single independent electrons, while the formation of pairs is an essential feature of the theory of Heitler and London.

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  1. 1

    see Hunter and Samuel, J. Chem. Soc., 1180 (1934); Lessheim and Samuel, Proc. Ind. Acad. Sci. (Bangalore), 1, 623 (1935), and the literature mentioned in these papers.

  2. 2

    Lessheim and Samuel, Phil. Mag., 21, 41 (1936); Asundi and Samuel, Proc. Phys. Soc., 48, 27 (1936); Proc. Ind. Acad. Sci. (Bangalore), 2, 30 (1935); 3, 466 (1936); Asundi, Jan Khan, and Samuel, Proc. Roy. Soc., in press, and literature mentioned there.

  3. 3

    Hunter and Samuel, Chem. and Ind., 54, 31, 467, 635. (1935); Rec. trav. chim., 54, 114 (1935), and literature mentioned there.

  4. 4

    J. Chem. Soc., 1709 (1935).

  5. 5

    cf. Stuart, ” Molekülstruktur,” p. 114 (1934).

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