Tables of physical and chemical constants and some mathematical functions / by G.W.C. Kaye and T.H. Laby.

  • G. W. C. Kaye
Date:
[1941]
Catalogue details

Licence: Public Domain Mark

Credit: Tables of physical and chemical constants and some mathematical functions / by G.W.C. Kaye and T.H. Laby. Source: Wellcome Collection.

    138/200 (page 126)
    IONIZATION POTENTIAL RESONANCE AND IONIZATION POTENTIALS When an electron collides with an atom of gas for relative velocities below a certain value, the collision is elastic and the electron rebounds from the atom, but for higher velocities there is an absorption by the atom of the energy of the electron. In general there are two types of inelastic collision, one in which an electron in the atom undergoes an interorbital transition and the other in which an electron is removed from the atom. The work done, measured in electron volts, to ionize the atom is the ionization potential, and similarly the work to displace the electron is the resonance potential. The first or principal ionizing potential is the energy necessary to remove an electron from the lowest state of the atom so as to produce the lowest state of the ion from which it is built, e.g. the energy required to remove one of the electrons from the lowest state (i S2 1S0) of the helium atom is the first ionizing potential of helium. The second ionizing potential is the work done in removing the second electron in its lowest state from the atom. That is, for example, the work done in removing the remaining i S 2Sj electron from the helium atom. Ionizing potentials can be determined (i) by direct observation of the potential required to produce ionization, and (2) indirectly by determining from the conver¬ gence limit of the optical spectra the amount of energy given out when an electron drops from infinity to the normal position of the valence electron. Ye — (c2h/io8)v volt e.s.u., where v cm.-1 is the wave number of the spectral line, i.e. V = 1*2385 X io~4 X v volt. Values given in the following table have been calculated by this method. The meaning of the symbols is given on p. 124, under “ Spectral Terms.” References :—Richtmeyer, “ Introduction to Modern Physics ” ; Bacher and Goudsmit, “ Atomic Energy States.” FIRST IONIZATION POTENTIALS AND LOWEST SPECTRAL TERMS OF THE ELEMENTS Ion. Pot. Term. Ion. Pot. Term. Ion. Pot. Term. Term. Term. H I3‘584 2S* Ca 6-n % ¥ 6-5 2D* Ce 3h4 Os 5F>4 He 24-564 % Sc 6-7 2D3 Zr 6-94 3f2 Pr 410,4 Os 6f5 Li 5’39 2Si Ti 6-83 3f2 Cb 6Dj Nd 5l6 Ir 4Fj? Be 9-32 % V 6-78 4F$ Mo 7-37 7S3 11 6Ly- Pt 3d3 B 8-31 2P1 Cr 6-76 7s3 Ma 6D? Sa 7k4 Pt % C 11-27 3Po Mn 7-43 6Sf Ru 5f5 Eu 8Hf Au 2S| N 14-54 4S? Fe 7-85 5D, Rh 7.7 4F| Gd 9D0 Hg % O 13-60 3P2 Co 8-5 4F? Pd 8-3 % Tb 8Hv Tl 2PI F 18-67 2P§ Ni 7-63 3f4 Ag 7-56 2S^ Dy 7K10 Pb 3Po Ne 21-56 % Cu 7-70 2Sj Cd 8-98 % Ho 6L¥- Bi 4Sf Na 5-i4 2S.t Zn 9-38 4S0 In 5-78 2P* Er 5Fio Po 3P2 Mg 7-64 % Ga 5'99 2PI Sn 7-32 3Po Tu 4K-V- —■ 2P A1 5-98 2P* Ge 8-n 3P(> Sb 8-5 4S* Yb 3h6 Rn % Si 8-15 3Po As 10 4S| Te 3P2 Lu 2D§ — 2S* P 4Ss Se 9-5 3P2 I 10 2P1 Hf 3f2 Ra % S 10-3 3P2 Br 11-85 2P'2 Xe 12-127 % Ta 4Fa Ac 2D? Cl 13-01 2p.? Kr 14-00 % Cs 3-88 2Sj W 5F)o Th 3f2 A 15-75 % Rb 4-176 2S* Ba 5-21 % Re 6Sf Pa 4F3 K 4-34 2Si Sr 5-690 % Lei 2D| Re 6D* U 5F)0 V. D. H. ELECTRONIC CHARGE Historical.—The electronic charge, e e.s.u., was measured in 1897 by J. S. Townsend, and in 1898 by J. J. Thomson by finding the average charge in a cloud of drops. The total charge was found, and Stokes’s law applied to obtain the average size and total number of drops. H. A. Wilson (1903) pointed out that if vx is the velocity of a drop falling freely, and vz its velocity when acted upon by a vertical electric field (X), then §7kz3(/o — <7)g — 677^^, and neX = 6TT7](z>2—v1)a = {162 n^^v^v^—v^Kp — a)gp where ne is the charge of the drop.