Showing papers on "Chemical bond published in 1976"
TL;DR: In this paper, the cell reactions between lithium and several transition metal oxides and sulfides have been found to produce ternary phases and not the formation of lithium oxide or sulfide as previously proposed.
Abstract: The cell reactions between lithium and several transition metal oxides and sulfides have been found to produce ternary phases and not the formation of lithium oxide or sulfide as previously proposed. These reactions, at 25°C, take place with essential retention of the crystalline lattice, thus facilitating secondary cathodic behavior. It is found that cell reversibility is optimized when no chemical bonds are broken during discharge, that is, where ternary phases are formed by an intercalation reaction and where a broad range of nonstoichiometry exists as in the system . Where some chemical bonds are broken as for and partial or difficult reversibility is found, but when all the bonds are broken as for example in , the cell only exhibits primary characteristics.
613 citations
TL;DR: In this article, a bond-valence analysis of the repulsion leads to the conclusion that strong and weak hydrogen bonds are different in kind, the stronger ones involve strain and are linear while the weaker ones (O-O greater than 2.7 A) have an extra degree of freedom and are generally bent.
Abstract: The asymmetry of hydrogen bonds arises from the repulsion between the O atoms forming the bonds. A bond-valence analysis of the repulsion leads to the conclusion that strong and weak hydrogen bonds are different in kind, the stronger ones (O-O less than 2.7 A) involve strain and are linear while the weaker ones (O-O greater than 2.7 A) have an extra degree of freedom and are generally bent. The strength of the hydrogen bond is determined by a number of factors such as the requirement that the bond valences around each atom add up to the atomic valence, a tendency for the O-O distance to be close to 2.7 A, and by crystal-packing considerations which often lead to the formation of bent, and hence weaker, hydrogen bonds. The bond-valence analysis correctly predicts the observed correlations between H⋯O distance and O-H-O angle. The frequency with which various hydrogen-bond configurations are observed in crystals is used to propose a method for determining hydrogen-bond energies. This analysis of hydrogen bonding leads to an understanding of the lengthening of hydrogen bonds in high-pressure ices and to proposals for hydrated ion structures which can be used, for example, to predict the acid strengths of anions and to show that in neutral aqueous solutions the oxygen atoms of complex anions each hydrogen-bond to two or three water molecules.
462 citations
TL;DR: In this article, relativistic and non-relativistic Hartree-Fock one-centre expansion calculations including valence s and p orbitals are reported for CuH, AgH and AuH molecules.
155 citations
154 citations
TL;DR: In this article, the first-row transition-metal monosulfides and alkaline-earth chalcogenides were studied by means of X-ray photoelectron spectroscopy.
126 citations
TL;DR: In this paper, the largest basis set used, split shell with d orbitals on carbon (SS + d), gives an optimized geometry of r(C--Li) = 2.021 A.
Abstract: SCF calculations are reported for CH/sub 3/Li using several basis sets. The largest basis set used, split shell with d orbitals on carbon (SS + d), gives an optimized geometry of r(C--Li) = 2.021 A, r(C--H) = 1.089 A, and
123 citations
120 citations
94 citations
TL;DR: In this paper, the shear strength of polycrystalline Ag, Cu, Ni, and Fe contacts on clean (0001) sapphire has been studied in ultrahigh vacuum.
Abstract: The shear strength of polycrystalline Ag, Cu, Ni, and Fe contacts on clean (0001) sapphire has been studied in ultrahigh vacuum. Both clean metal surfaces and surfaces exposed to O2, Cl2, and C2H4 were used. The results indicate that there are two sources of strength of Al2O3-metal contacts: an intrinsic one that depends on the particular clean metal in contact with Al2O3 and an additional one due to intermediate films. The shear strength of the clean metal contacts correlated directly with the free energy of oxide formation for the lowest metal oxide, in accord with the hypothesis that a chemical bond is formed between metal cations and oxygen anions in the sapphire surface. Contacts formed by metals exposed to chlorine exhibited uniformly low shear strength indicative of van der Waals bonding between chlorinated metal surfaces and sapphire. Contacts formed by metals exposed to oxygen exhibited enhanced shear strength, in accord with the hypothesis that an intermediate oxide layer increases interfacial strength.
91 citations
TL;DR: The trimer spectra indicate the unpaired electron in these molecules have predominantly s rather than p character as mentioned in this paper, indicating the trimers are not merely van der Waals adducts but involve chemical bonding.
Abstract: E.S.R. spectra assigned to Na3 molecules have been obtained by codepositing sodium atoms and diluent argon on a sapphire surface loosely coupled to a liquid helium cryostat and warmed by a heat leak, to allow aggregation before the alkali atoms are frozen into the argon matrix. The trimer spectra under these conditions were much more intense than the residual atom spectra. The trimer spectra indicate the unpaired electron in these molecules has predominantly s rather than p character. Approximately 95 per cent of the 3s spin density is equally distributed between two of the alkali atoms, with only about 7 per cent of the spin density on the third atom. The trimers thus are not merely van der Waals adducts but involve chemical bonding. Both a covalent molecular orbital model for linear or obtuse isosceles geometry and an ionic charge-transfer model giving M2 +M- or M+M2 - appear qualitatively consistent with the spectra.
TL;DR: A general discussion of quadratic potential constants which describe the interatomic forces for a molecule in its equilibrium configuration, and some problems associated with the evaluation of the potential constants are described in this paper.
Abstract: A general discussion is presented of quadratic potential constants which describe the interatomic forces for a molecule in its equilibrium configuration, and some problems associated with the evaluation of the potential constants are described. Current bonding models of both cyanide and carbonyl complexes of the transition metals are discussed, and various constants for different complexes are tabulated. The results suggest that the usual localized molecular orbital model is deficient in discussing the bonding interactions. (BLM)
TL;DR: In this article, relativistic and non-relativistic Hartree-Fock calculations including np12 and np32 orbitals in the valence MO are reported for the molecules BH, AlH, GaH, InH and TlH.
TL;DR: In this article, a theoretical description of the valence band structure and chemical bonding for a series of non-transition-metal layer compounds is developed which is consistent with calculated charge densities, densities of states, and with the experimental crystal-structure data and photoemission measurements.
Abstract: A theoretical description of the valence-band structure and chemical bonding for a series of non-transition-metal layer compounds is developed which is consistent with calculated charge densities, densities of states, and with the experimental crystal-structure data and photoemission measurements.
TL;DR: In this article, the chemical bonding in AlB2-type metal diboride phases is considered from a crystal chemical viewpoint, and the ability of metals to deform from a spherical shape appears to be very important in explaining why the diborside is formed by such a wide variety of metals.
Abstract: The chemical bonding in AlB2-type metal diboride phases is considered from a crystal chemical viewpoint. The ability of metals to deform from a spherical shape appears to be very important in explaining why the diboride is formed by such a wide variety of metals. Crystal chemical parameters are used to compare relative bond strengths.
Book•
01 Jun 1976
TL;DR: The Foundations of Chemistry as mentioned in this paper is a collection of chemical properties, formulas and composition stochastic geometry, and reactions in aqueous solvices, as well as some types of chemical reactions.
Abstract: CONTENTS: The Foundations of Chemistry. Chemical Formulas and Composition Stoichiometry. Chemical Equations and Reactions Stoichiometry. Some Types of Chemical Reactions. The Structure of Atoms. Chemical Bonding. Molecular Structure and Covalent Bonding Theories. Molecular Orbitals in Chemical Bonding. Reactions in Aqueous Solutions I: Acids, Bases and Salts. Reactions in Aqueous Solutions II: Calculations. Gases and the Kinetic Molecular Theory. Liquids and Solids. Solutions. Chemical Thermodynamics. Chemical Kinetics. Chemical Equilibrium. Ionic Equilibria I: Acids and Bases. Ionic Equilibria II: Buffers and Titration Curves. Ionic Equilibria III: The Solubility Product Principle. Electrochemistry. Metals I: Metallurgy. Metals II: Properties and Reaction. Some Nonmetals and Metalloids. Co-ordination Compounds. Nuclear Chemistry. Organic Chemistry I: Formulas, Names and Properties. Organic Chemistry II: Molecular Geometry and Reactions. QUALITATIVE ANALYSIS: Metals in Qualitative Analysis. Introduction to Laboratory Work. Analysis of Cation Group I. Analysis of Cation Group II. Analysis of Cation Group III. Analysis of Cation Group IV. Analysis of Cation Group V. Ionic Equilibria in Quantitative Analysis
IBM1
TL;DR: In this article, it was shown that adsorption of organic molecules on semiconducting ZnO surfaces produces bonding shifts of molecular energy levels which indicate chemisorption via π and lone-pair orbitals; and nearly uniform extramolecular relaxation/polarization shifts of the adsorbate valence orbital energies.
TL;DR: The electron structure of acetylene, ethylene and benzene chemisorbed on the normal (1 × 1) and reconstructed (5 × 1)-clean surfaces of Ir(100) has been studied as a function of surface coverage and adsorption temperature using UPS-photoelectron spectroscopy and low energy electron-diffraction as discussed by the authors.
TL;DR: In this article, the cell reactions between lithium and several transition metal oxides and sulfides have been found to produce ternary phases and not the formation of lithium oxide or sulfide as previously proposed.
Abstract: The cell reactions between lithium and several transition metal oxides and sulfides have been found to produce ternary phases and not the formation of lithium oxide or sulfide as previously proposed. These reactions, at 25°C, take place with essential retention of the crystalline lattice, thus facilitating secondary cathodic behavior. It is found that cell reversibility is optimized when no chemical bonds are broken during discharge, that is, where ternary phases are formed by an intercalation reaction and where a broad range of nonstoichiometry exists as in the system . Where some chemical bonds are broken as for and partial or difficult reversibility is found, but when all the bonds are broken as for example in , the cell only exhibits primary characteristics.
TL;DR: An approximate molecular orbital theory for bound positrons is presented in this paper, which is semi-empirical and the parameterization scheme is based upon some very sparse data together with plausible interpolation ideas.
Abstract: An approximate molecular orbital theory for bound positrons is presented. The theory is semiempirical and the parameterization scheme is based upon some very sparse data together with plausible interpolation ideas. The CNDO/2 approach is followed for the positron, and that method is used also for the purely electronic part of the theory; molecules comprising first-row atoms are considered. The calculations yield fully self-consistent positronic and electronic molecular orbitals, as well as positron and positronium affinities of molecules. Results for over 60 molecules are presented. General features of positron and positronium binding are discussed. Positronium appears to be stable to split-off in molecules in which it replaces hydrogen; for weak acids, a good correlation is found between acid strength and positron affinity for the anion; however, the positron does not appear to be a typical electrophile in aromatic addition reactions. Some justification of the approach used is provided by agreement or consistency of the calculated results with some recent experimental observations. For smaller molecules, positronium bond strengths in PsO/sub 2/, PsNO, and PsNO/sub 2/ (0, 0, 1.95 eV, respectively) seem to be consistent with relative tendencies of gaseous O/sub 2/, NO, and NO/sub 2/ molecules to quench triplet positronium by chemicalmore » combination as opposed to spin conversion (0, 0, 25%) as reported by Goldanskii and co-workers. Quenching cross secions for these three molecules as reported by Chuang and Tao (0.002 65, 0.008 45, and 26 A/sup 2/, respectively) seem to suggest the stability of PsNO/sub 2/ but not PsO/sub 2/ and PsNO, in agreement with our calculations.« less
TL;DR: The infrared absorption of argon and hydrogen chloride mixtures has been re-examined in the spectral region 2860-3010 cm−1 (the missing Q branch region) over the temperature range 195-298°K as mentioned in this paper.
Abstract: The infrared absorption of argon (200–760 torr) and hydrogen chloride (2–6 torr) mixtures has been re‐examined in the spectral region 2860–3010 cm−1 (the missing Q branch region) over the temperature range 195–298°K. The temperature dependence of two absorption features of the Ar⋅HCl complex, at 2887 and 2879 cm−1, lead to a bond energy estimate that depends upon the assumptions made about the internal degrees of freedom of the complex. Agreement with experiment can be reached for well depths near 1.2 kcal/mole, a result that is relatively insensitive to the choices of the vibrational frequencies and anharmonicities but which does depend upon the extent to which the energy level manifolds are truncated to avoid molecular excitation in excess of the bond energy. This bond energy contrasts with the commonly accepted value of 0.4 kcal/mole; the possible origin of the disparity is considered.
TL;DR: In the present paper, the authors will compare the actual correlative abilities of the HMO, SCF-MO, and the Pauling theories by statistical techniques.
Abstract: In the present paper, the authors will compare the actual correlative abilities of the HMO, SCF-MO, and the Pauling theories by statistical techniques.
IBM1
TL;DR: In this article, ultraviolet photo-emission studies of HCOOH decomposition on ZnO (1 1 00) at 120 and 300 K were performed, and the reaction products remaining on the surface include CO and atomic O.
TL;DR: The theoretical and experimental results of the study of hydrogen-bonded complexes are examined from the standpoint of the donor-acceptor nature of hydrogen bonds in this paper, and the linear correlation between the energy of charge transfer and the hydrogen bond energy is analyzed and validated.
Abstract: The results of studies on the dipole moments and the thermodynamics of the formation of complexes with an intermolecular hydrogen bond are reviewed and the nature of the relation between the energies and lengths of intermolecular hydrogen bonds is examined. The enthalpy?entropy relations for the formation of hydrogen-bonded complexes and the linear correlation between the energy of charge transfer and the hydrogen bond energy are analysed and validated. The theoretical and experimental results of the study of hydrogen-bonded complexes are examined from the standpoint of the donor?acceptor nature of hydrogen bonds. The bibliography includes 240 references.
TL;DR: In this paper, the basic repeat unit of the zig-zag metal atom chain was found to include three crystallographically independent Pt atoms, and a discussion of water molecule hydrogen bonding to cyanide ligands was included.
Abstract: The potassium deficient cyanoplatinate complex, K/sub 1.75/Pt(CN)/sub 4/.1.5H/sub 2/O was prepared and the results of a single-crystal neutron diffraction study are reported. The basic repeat unit of the zig-zag metal atom chain was found to include three crystallographically independent Pt atoms. Bond angles and lengths are reported; a discussion of water molecule hydrogen bonding to cyanide ligands is included. (DDA)
TL;DR: In this paper, the experimental X-ray emission spectra of titanium carbide, nitride and oxide have been obtained and the results of these calculations are in good agreement with the Xray spectroscopy data and offer a reasonable explanation of the experimental spectra.
TL;DR: In this paper, a study of the chemical trends displayed by lunar armalcolites has been made in conjunction with single-crystal X-ray structure refinements of lunar and synthetic armsalcolite in order to assess the possible importance of Ti3+ in lunar and to characterize the effects of cation substitutions on the structure.
TL;DR: In this paper, the microwave spectra of C2HDO2 and C2D2O2 have been obtained and assigned in the range from 18 to 40 GHz, and the determined rotational constants for C2 HDO2 were: A = 23857.40 ± 0.36, B = 6075.89 ± 0.09, and C = 4849.65 MHz; and for C 2D2
TL;DR: In this paper, the participation of the d-electrons in chemical bonding and their role in the chemical bonding was studied and it was shown that with increasing metal atomic number within one group the d sub-band increases by ca. 2 eV in group I and ca. 1 eV for group II.