Electronegativity based on the simple bond charge model

A single physical interpretation of the various electronegativity scales of Pauling, Mulliken and Gordy is suggested, based on the simple bond charge (SBC) model of Parr and Borkman for the covalent bond. With a charge partition determined from vibrational frequencies, the SBC model is shown to account for the covalent bond energy in single-bonded homonuclear diatomic molecules and diamond-type crystals. The binding energy to the atom of a bond-electron in the single-bonded homonuclear diatomic molecules agrees with Mulliken's electroaffinity, and provides a definition for electronegativity. Gordy's empirical relation between the bond-stretching force constant and electronegativity is explained. It is then suggested that the physical effect underlying Pauling's thermochemical formula for electronagativity is the location of the bond charge in the heteronuclear molecule. The deviation of Pauling's formula from experiment in the case of the alkali hydrides can then be explained.     

A molecular electrostatic potential bond critical point model for atomic and group electronegativities

A consistent set of atomic electronegativities of main block and d-block transition elements has been obtained from the position and value of the molecular electrostatic potential bond critical point of the C-E bond of a methyl-element-hydride system, H(3)C-EH(n) (E is an element and n = 0, 1, 2, 3, 4, and 5 depending on the position of E in the periodic table). The new scale shows very good agreement with the popular electronegativity scales such as Pauling, Allen, Allred-Rochow, Mulliken, and Sanderson scales of electronegativity, especially for the main block elements. The present scale of electronegativity for transition elements is expected to be more accurate than the previously derived values because of a more consistent approach. Further, the same approach has led to the evaluation of group electronegativities when the hydrogens of E are replaced by other substituent groups. These group electronegativity values are found to correlate well with Inamoto and Mullay scales.     

Molecular structure and Bader's theory

 It is shown that a supposed catastrophe of Bader's theory of atoms in molecules, suggested by Cassam-chena? and Jayatilaka [Theor Chem Acc (2001) 105: 213] is merely a consequence of the approximate character of the adiabatic Born–Oppenheimer theory of molecular structure, and that nonadiabatic approaches could be in accordance with Bader's ideas. Received: 4 April 2001 / Accepted: 5 September 2001 / Published online: 3 June 2002     

Towards universal substituent constants: Parameterizing bond critical point properties with electronegativity descriptors

The properties of substituents have long been quantified by their effect elsewhere in a molecule. Ideally, intrinsic properties detailing the true properties of a substituent would be used. These properties are ideally transferable between molecules, to be robust and applied in different situations. Through a study on the bond critical point (BCP) properties of 117 substituents and 17 substrates we find that BCP properties from the quantum theory of atoms in molecules are not transferable between different bonded atoms. However, a substituent's changing electronegativity between substrates help quantify the observed variation. The relationship between changing electronegativities and critical point properties enables development of a relationship to predict critical point properties between a substituent and a new substrate, using only the electronegativity of a substituent attached to hydrogen, and the critical point property between the substituent and H.     

Bader's interatomic surfaces are unique

 In this work we comment on the statement about the nonuniqueness of the solution of Bader's equation for defining atoms in molecules reported in the article of P. Cassam-Chena? and D. Jayatilaka in Theoretical Chemistry Accounts (2001) 105: 213–218 Received: 10 May 2001 / Accepted: 7 September 2001 / Published online: 3 June 2002     

Electronegativity estimator built on QTAIM‐based domains of the bond electron density

The electron localization function, natural localized molecular orbitals, and the quantum theory of atoms in molecules have been used all together to analyze the bond electron density (BED) distribution of different hydrogen‐containing compounds through the definition of atomic contributions to the bonding regions. A function, g_AH, obtained from those contributions is analyzed along the second and third periods of the periodic table. It exhibits periodic trends typically assigned to the electronegativity (χ), and it is also sensitive to hybridization variations. This function also shows an interesting S shape with different χ‐scales, Allred–Rochow's being the one exhibiting the best monotonical increase with regard to the BED taken by each atom of the bond. Therefore, we think this χ can be actually related to the BED distribution. © 2014 Wiley Periodicals, Inc.     

电负性均衡

电负性是分子中一个原子把电子拉向它自身的能力,是化学理论的基本概念之一。继Pauling建立第一个电负性标度后,提出了众多的电负性标度。只是在密度泛函理论的基础上,电负性概念和电负性均衡原理,才被精密地论证。近二十多年来,电负性理论的重要发展是:应用电负性均衡模型或方法,可以快速地计算分子体系的电荷分布,从而确定分子的其他性质,甚至包括分子的结构和反应性指标。通常的电负性均衡方法只把分子划分到原子区域,虽然简单直观,但其精度和应用范围受到限制。原子与键电负性均衡方法,把分子划分到包括原子区域、化学键区域和孤对电子区域,能够较快速精密地计算分子的电荷分布和其他性质,并被应用到构建新一代可极化或浮动电荷力场的探索中,有广阔的应用前景。     

电负性研究(Ⅱ)—氢的电负性

氢的电负性值是氢元素性质的重要参数，１９３２年Pauling犤１～３犦定量确定氢的相对电负性值等于２．１，１９６１年Allred犤４，５犦用更准确的实验数据对Paul－ing电负性标度进行了修正，氢的电负性值被确定为２．２，目前这两个数值都在采用。元素的电负性值是与元素的性质紧密相关的，一个合适的电负性标度应该至少反映所有重要元素的电负性值，氢的化合物比任何其它元素都多，理应有一个基本的准确电负性值，然而一些电负性标度中却缺乏这样的数据。在Murphy等四人犤６犦最近发表的论文中，对Pauling电负性标度又进行了深入考查与…     

Electronegativity and Molecular Properties

The paradigm that the properties of the atoms determine the properties of the molecules that they form is systematically presented. To this end, three types of atomic properties are differentiated: (a) those that can be determined directly by spectroscopy, (b) those based on theoretical concepts, and (c) those that can be assigned to the atoms interacting in molecules. On the basis of the electronegativity values of the atoms, which can be determined from spectroscopic data together with the assumption that the electronegativities are equalized in bonds, partial charges of the atoms in molecules are determined. These partial charges are correlated with ESCA data and proton affinities. In addition, simple expressions are given for the reliable estimation of bond lengths, bond energies, and force constants. For corrigendum see DOI: 10.1002/anie.199607811     

Electronegativity under Confinement

The electronegativity concept was first formulated by Pauling in the first half of the 20th century to explain quantitatively the properties of chemical bonds between different types of atoms. Today, it is widely known that, in high-pressure regimes, the reactivity properties of atoms can change, and, thus, the bond patterns in molecules and solids are affected. In this work, we studied the effects of high pressure modeled by a confining potential on different definitions of electronegativity and, additionally, tested the accuracy of first-order perturbation theory in the context of density functional theory for confined atoms of the second row at the Hartree–Fock level. As expected, the electronegativity of atoms at high confinement is very different than that of their free counterparts since it depends on the electronic configuration of the atom, and, thus, its periodicity is modified at higher pressures.     

Theoretical electron density distributions for Fe- and Cu-sulfide earth materials: a connection between bond length, bond critical point properties, local energy densities, and bonded interactions

Bond critical point and local energy density properties together with net atomic charges were calculated for theoretical electron density distributions, rho(r), generated for a variety of Fe and Cu metal-sulfide materials with high- and low-spin Fe atoms in octahedral coordination and high-spin Fe atoms in tetrahedral coordination. The electron density, rho(rc), the Laplacian, triangle down2rho(rc), the local kinetic energy, G(rc), and the oxidation state of Fe increase as the local potential energy density, V(rc), the Fe-S bond lengths, and the coordination numbers of the Fe atoms decrease. The properties of the bonded interactions for the octahedrally coordinated low-spin Fe atoms for pyrite and marcasite are distinct from those for high-spin Fe atoms for troilite, smythite, and greigite. The Fe-S bond lengths are shorter and the values of rho(rc) and triangle down2rho(rc) are larger for pyrite and marcasite, indicating that the accumulation and local concentration of rho(r) in the internuclear region are greater than those involving the longer, high-spin Fe-S bonded interactions. The net atomic charges and the bonded radii calculated for the Fe and S atoms in pyrite and marcasite are also smaller than those for sulfides with high-spin octahedrally coordinated Fe atoms. Collectively, the Fe-S interactions are indicated to be intermediate in character with the low-spin Fe-S interactions having greater shared character than the high-spin interactions. The bond lengths observed for chalcopyrite together with the calculated bond critical point properties are consistent with the formula Cu+Fe3+S2. The bond length is shorter and the rho(rc) value is larger for the FeS4 tetrahedron displayed by metastable greigite than those displayed by chalcopyrite and cubanite, consistent with a proposal that the Fe atom in greigite is tetravalent. S-S bond paths exist between each of the surface S atoms of adjacent slabs of FeS6 octahedra comprising the layer sulfide smythite, suggesting that the neutral Fe3S4 slabs are linked together and stabilized by the pathways of electron density comprising S-S bonded interactions. Such interactions not only exist between the S atoms for adjacent S8 rings in native sulfur, but their bond critical point properties are similar to those displayed by the metal sulfides.     

Salting out near the critical point

The salting out of solid solutes near the critical point of the solvent is investigated using the results of a previous paper (J. Phys. Chem. B 2006, 110, 24077) on the fluctuation theory of salting out. It is found that the salting out coefficient at infinite dilution of cosolvent is approximately proportional to the compressibility of the solvent and is consequently quite large near the critical point. No estimate is given for the range of cosolvent concentrations over which the infinite dilution slope might be a good approximation. Far from the critical point, it is known to be a good approximation over a considerable cosolvent concentration range.     

Electronegativity: Quantum observable

The question whether electronegativity may be considered as quantum observable is responded in positive by a special ionization‐affinity wave function construction within the fermionic Fock space for the valence state of a chemical system. The present approach consecrates electronegativity as the minus eigen‐energy of the unperturbed occupied valence state involved in addition and release of electrons by atoms‐in‐molecules interactions. This way, the earlier crisis raised by Bergmann and Hinze concerning the assignment of chemical potential to electronegativity quantification is here solved in the favor of Parr density functional picture. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Absolute Electronegativity in Gas

A variational formula has been obtained for the relationship between total electronic energy and absolute electronegativity.     

Electronegativity in Quantum Chemistry

The possibility is discussed for determination of chemical potential (electronegativity) of an electron-nucleus system in terms of the quantum-mechanical density functional theory (DFT). The principle of complete leveling of chemical potentials of natural orbitals, formulated in the framework of DFT, cannot be regarded now as justified. The calculation of electronic chemical potential via difference schemes still remains the only procedure suitable for estimation of this quantity by quantum-chemical methods.     

Liquid-gas coexistence and critical point shifts in size-disperse fluids

Specialized Monte Carlo simulations and the moment free energy (MFE) method are employed to study liquid-gas phase equilibria in size-disperse fluids. The investigation is made subject to the constraint of fixed polydispersity, i.e., the form of the "parent" density distribution rho(0)(sigma) of the particle diameters sigma, is prescribed. This is the experimentally realistic scenario for, e.g., colloidal dispersions. The simulations are used to obtain the cloud and shadow curve properties of a Lennard-Jones fluid having diameters distributed according to a Schulz form with a large (delta approximately 40%) degree of polydispersity. Good qualitative accord is found with the results from a MFE method study of a corresponding van der Waals model that incorporates size dispersity both in the hard core reference and the attractive parts of the free energy. The results show that polydispersity engenders considerable broadening of the coexistence region between the cloud curves. The principal effect of fractionation in this region is a common overall scaling of the particle sizes and typical interparticle distances, and we discuss why this effect is rather specific to systems with Schulz diameter distributions. Next, by studying a family of such systems with distributions of various widths, we estimate the dependence of the critical point parameters on delta. In contrast to a previous theoretical prediction, size dispersity is found to raise the critical temperature above its monodisperse value. Unusually for a polydisperse system, the critical point is found to lie at or very close to the extremum of the coexistence region in all cases. We outline an argument showing that such behavior will occur whenever polydispersity affects only the range, rather than the strength of the interparticle interactions.