Inorganic Chemistry of the Main-Group Elements: Volume 1 (Specialist Periodical Reports - Inorganic Chemistry of the Main-Group Elements)

Product description Excerpt. © Reprinted by permission. All rights reserved. Inorganic Chemistry of the Main-group Elements Volume 1A Review of the Literature Published Between July 1971 and September 1972By C. C. AddisonThe Royal Society of ChemistryCopyright © 1973 The Royal Society of ChemistryAll rights reserved.ISBN: 978-0-85186-752-6ContentsChapter 1 Elements of Group I By R. J. Pulham, 1, Chapter 2 Elements of Group II By R. J. Pulham, 31, Chapter 3 Elements of Group III By G. Davidson, 53, Chapter 4 Elements of Group IV By P. G. Harrison and P. Hubberstey, 143, Chapter 5 Elements of Group V By N. Logan and D. B. Sowerby, 231, Chapter 6 Elements of Group VI By M. G. Barker, 324, Chapter 7 The Halogens and Hydrogen By M. F. A. Dove, 373, Chapter 8 The Noble Gases By M. F. A. Dove, 412, Author Index, 421, CHAPTER 1Elements of Group IBY R. J. PULHAMIn this chapter individual references which are inter-related are grouped together to make a section and, therefore, reference to several alkali metals may feature in a single section. Each reference, however, appears once only within this chapter so that if described in one section, it will not be duplicated in any other. Single references to topics are presented systematically in the section on the appropriate metal.The elements of Groups I and II are so closely linked in some instances that a section describing them jointly is presented to avoid duplication in Chapter 2. Such a case is the section on 'Molten Salts' which covers the chemistry of the molten salts of both Groups I and II but is presented only in this chapter. A similar situation exists with the section on 'Solutions in Liquid Ammonia' and also with a few other isolated references.1 The Alkali MetalsIsolation. — The preparation of lithium, (like calcium, strontium, and barium) may be achieved by reduction of its fluoride or oxide by hydrogen in the presence of noble metals. The method seems applicable, in principle, to all alkali metals. A finely ground mixture of metal oxide (Li2O, CaO, SrO, or BaO) and noble metal (Pt, Pd, or Ir) is heated above 1100 °C in a stream of pure hydrogen. The noble metal functions as a catalyst in this reduction which is normally not possible. The required metal forms an intermetallic compound of composition AB2, AB3, AB5, and/or AB7, where A = Li, Ca, Sr, or Ba and B = Pt, Pd, or Ir. At higher temperatures and lower pressures (10-5 — 10-6 Torr) part of the more volatile component A volatilizes and is isolated by condensation.Vapours. — The vapour pressure of potassium up to the critical point (1925 ± 30 °C and 155 ± 15 bar) has been obtained by measuring the pressure needed to collapse a bubble of vapour in the liquid metal. The appearance and disappearance of the vapour bubble was followed by its effect on the resistance and thermo-power of the system. The tabulated data are largely summarized by the equation[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]The rate of ionization of alkali-metal atoms in flames of H2 + O2 + N2 has been measured using a quadrupole mass spectrometer to determine concentrations of each ion in the flame. The results confirm that the atoms, M, ionize by collision with flame gas molecules, X:M + X -> M+ + e- + XThe measured activation energy is, within experimental error, the ionization potential of the alkali metal. The associated cross-sections πσ2 are anomalously large, being similar for each metal and in the range 2.5 ± 1.1 × 10-16. The transfer of excitation energy in caesium vapour induced by collision with a molecule of nitrogen or hydrogen at 450 K has also been studied. The effective cross-sections (Å2)of the transfer of excitation energy from the 82P1/2 to the 82P3/2, 72P3/2, and 72D5/2 states of caesium are 55 ± 11, 1.8 ± 0.5, and 3.3 ± 1 for nitrogen and 80 ± 16, 4.7 ± 1.3, and 6.6 ± 2 for hydrogen, respectively. An indication of the electron density in ionized caesium vapour has been deduced from the emission spectrum and an increase in the intensity of certain spectral lines during the post-luminescence of the ionized vapour was attributed to the process of recombination.Theoretical Aspects. — An approximate equation of state for liquid metals, including the alkali metals, has been developed using a corrected entropy of melting (constant for all metals), the Lindemann law for melting, and a specific heat which has universal dependence on the ratio of the temperature to the melting temperature. A mean spherical model for the structure of liquid metals is also proposed, applicable to sodium, which is a perturbation of the Percus–Yevick hard-sphere model.There are several reports on alkali-metal molecules. The bond energies (calculated by LCAO MO) in small clusters of lithium atoms are shown to change with both the number of atoms in the cluster and their configuration. A previously developed valence-electron model is used in theoretical calculations on states of the molecules Li2, Na2, K2, LiNa, LiK, and NaK, which dissoc