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 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.     

Physical Interpretation of the Electronegativity

An additivity scheme of electronegativities of univalent substituents has been proposed on the basis on the Van Vleck orbital model of valence states of atoms. The electronegativity of any organic or heteroelement-containing substituent can be calculated from the orbital electronegativities and hardnesses of atoms constituting that substituent. The proposed additivity scheme is the most consistent among those currently available for calculation of orbital electronegativities of univalent substituents. The scheme was substantiated with the aid of quantum-chemical scale of group electronegativities.     

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 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 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.     

Electronegativity and hardness in the chemical approximation

The chemical electronegativity of an atom (Mulliken definition) has been identified with the average value of χ, the electronegativity function given by the rigorous density functional theory. An appropriate definition of hardness is developed, and a scale of hardness for bonded atoms is proposed. The electrodynamical atom model is demonstrated to produce a simple relation between atomic hardness and size. Electronegativity has been calculated for bonded atoms in a variety of molecules and crystals, covalent and ionic, without any specific approximation for the energy function E(q). Expressions for the electronegativity of a molecule have been derived and critically discussed.     

一种新的电负性标度

提出了一种新的电负性标度计算方法 ,表达了原子在分子中吸引电子的能力 ,基本反映了元素周期性规律。     

再论电负性标度的发展

电负性是化学中的一个重要概念,在基础化学课程中起着关键作用。本文将电负性研究过程分为三个阶段,简述了关于电负性标度的认识不断深入、逐步发展的过程,在讨论不同电负性标度的基础上,着重讨论了绝对电负性标度和Pauling类型电负性标度的差别性、Allen电负性标度及其修正的Rahm标度等,对深刻理解电负性标度这一基本概念及促进无机化学教学内容的改革均有重要意义。     

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.     

In-Situ Electronegativity and the Bridging of Chemical Bonding Concepts

One challenge in chemistry is the plethora of often disparate models for rationalizing the electronic structure of molecules. Chemical concepts abound, but their connections are often frail. This work describes a quantum-mechanical framework that enables a combination of ideas from three approaches common for the analysis of chemical bonds: energy decomposition analysis (EDA), quantum chemical topology, and molecular orbital (MO) theory. The glue to our theory is the electron energy density, interpretable as one part electrons and one part electronegativity. We present a three-dimensional analysis of the electron energy density and use it to redefine what constitutes an atom in a molecule. Definitions of atomic partial charge and electronegativity follow in a way that connects these concepts to the total energy of a molecule. The formation of polar bonds is predicted to cause inversion of electronegativity, and a new perspective of bonding in diborane and guanine−cytosine base-pairing is presented. The electronegativity of atoms inside molecules is shown to be predictive of pK_a.     

Electronegativity and Bader's bond critical point

The electronegativities () of some 36 atoms/groups (including some 6 ionic ones) X are calculated from the atomic charges in the corresponding methyl species CH₃X that were obtained by applying Bader's theory of atoms in molecules. The numerical values of the for the various groups studied are reasonable and correlate linearly with the two existing experimental scales for group electronegativity, Inamoto's i scale and the ¹J_CC (ortho-ipso) coupling constants in the monosubstituted benzenes, to satisfactory extents. The relations between the values and some “critical properties” of the various CH₃X molecules considered are also studied. It is suggested that in a molecule PX, r_P/R where r_P is the distance of Bader's critical point on the bond PX of length R from the atom P or the binding atom of the group P can be a very good measure of the electronegativity of the atom/group X. © 1992 by John Wiley & Sons, Inc.     

超原子理论计算基团电负性的研究

依据Bratsch计算基团电负性的方程,根据Pauling原子电负性标度,提出了一种计算较大基团电负性的方法,该方法基于超原子思想。使用该方法做了大量的基团计算,并和引用其他文献计算结果做对比,结果表明提出的方法更加适用于计算较大的基团。     

一种新的轨道电负性标度

电负性是最重要的化学概念之一 ,1 932年由ＰａｕｌｉｎｇＬ提出 ,并把电负性定义为“原子在分子中吸引电子的能力”。由于这种能力不能用实验直接测定 ,所以不同的学者基于对电负性概念的不同理解 ,提出了不同的电负性标度。这些标度可以分为两类 ,一类与分子中原子的性质相联系 ,如Ｐａｕｌｉｎｇ标度Ｘｐ,Ａｌｌｒｅｄ Ｒｏｃｈｏｗ标度ＸＡ,Ｊａｆｆ啨标度ＸＪ。另一类与孤立原子的性质相联系 ,如Ｍｕｌｌｉｋｅｎ标度ＸＭ,Ａｌｌｅｎ标度Ｘｓｐｅｃ。两类标度的数值基本一致。　　上述各标度中 ,ＸＰ,ＸＡ,ＸＭ,ＸＪ 已为广大化学工作…