原子的价态电负性与价键轨道特性

电负性概念自Pauling提出以来,在化学学科中得到了广泛的应用,相继出现了多种经验或半经验的计算方法。Allred等将原子核作用于价电子的静电力定义为原子的电负性,使得电负性具有较直观的物理含义,是最广泛采用的标度之一。Mulliken将原子电负性定义为该原子的第一电离势和第一电子亲和能的平均     

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…     

电负性与原子价层轨道能

用密度泛函理论论证了原子价层轨道能与元素电负性之间的密切关系，说明如何用原子价层轨道能对元素电负性的概念进行解释，从而使周期表中元素电负性更容易被理解和计算。     

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。     

一种电负性新标度：基态自由原子价壳层电子平均吸引能

原子吸引价电子的总能力可由基态自由原子的价电子离子化能(TIE=Σn_iE_i)及其电子亲合能(EA)之和来度量。该和值亦称为总吸引能,记为TAE=Σn_iE_i+EA,此处E_i为基态自由原子价壳层电子的离子化能,Σn_i为与之相关的价壳层电子数,EA则是电子亲合能。所指出的新电负性标度χ_CL与总吸引能TAE除以原子价壳层电子数目Σn_i之值即平均吸引能成正比：χ_CL=0.1813 AAE=0.1813 TAE/Σn_i=0.1813(Σn_iE_i+EA)/Σn_i,进一步从原子总吸引能TAE可确定其价轨道电负性。     

电负性研究I．建立元素电负性标度的有效核电荷数方法

通过价层电离能、价键轨道能量用有效核电荷数法建立了周期表中90种元素的电负性新标度。X＝0。4123√－EV,该式表明电负性值与价键轨道能量的绝对值的平方根成正比,所得数值是一套无量纲的相对参数。元素电负性值随价态的升高与元素非金属性的增强相对应,元素电负性的大小不仅与单个成键电子腾,而且也与参加价键作用的多个电子甚至整个价层都有紧密的联系。氢的元素电负性值不同于Pauling值、等于1．52。用16种氢化物中键的额外离子能△′对（XA－XB）^2作图,两者之间确实具有良好的线性关系。本方法充分体现了目前公认的三大电负性标度的优点,该标度同时也是价层电子在价键状态下的一种能量标度,是对元素周期律的定量描述和反映。     

原子电负性的新研究

原子电负性是一应用十分广泛的重要物理量，已有很多表示方法，有关评论文章也很多。Pauling把电负性定为为“原子在分子中吸引电子的能力”。按Pauling电负性定义，键合原子不同，分子中原子吸收电子的能力也不同，因此原子电负性不是恒定值。为了     

原子价壳层电子量子拓扑指数与元素电负性的关系

在基态原子价壳层电子隐核图的基础上, 基于拓扑化学原理以及原子价壳层电子结构特征, 构建了原子价壳层电子量子拓扑指数(AEI), 它对基态原子实现唯一性表征, 结合原子价壳层电子平均化能(∑n_iE_i/∑n_i)等参数, 建立了一套新的元素电负性标度: X_N＝－0.588710AEI₁＋0.761214AEI₂＋0.154982(∑n_iE_i/∑n_i)－0.080929. 该式给出了周期表中氢至镅共95种元素的电负性, 结果表明新电负性标度X_N与Pauling电负性标度颇为一致. 进一步从原子价轨道量子拓扑指数确定了sp, sp², sp³杂化轨道的电负性. 新标度在元素和物质的结构-性质研究中具有一定的适用性.     

原子核强度电势和原子价层电量对元素电负性的标度

根据万有引力势与电势的关系式和系统的对比质电比(单位电量的质量)的物理意义, 定义了系统的强度电势——单位质量的电势. 研究表明, 元素电负性XSc与原子核在原子边界面上的强度电势Vic和价层电子电量qcj成线性关系. 采用回归分析法, 对周期表中除零族、氢及放射性元素之外的77种元素的Pauling电负性(XP)进行回归分析, 得到了一个无量纲的综合性的电负性计算公式, 相关系数(R=0.9844)和回归方程F检验的显著性水平(Sig.=0.0000)表明, XSc与Vic和qcj密切相关, 77种元素的拟合值与XP十分接近, 平均绝对误差仅为0.084; 并预测出较为合理的稀有气体元素的电负性. 用该式可以方便而更准确地计算除氢以外的所有元素的电负性; 同时也给出一条获取离子电负性和基团电负性的新途径.     

电负性研究Ⅰ.建立元素电负性标度的有效核电荷数方法

通过价层电离能、价键轨道能量用有效核电荷数法建立了周期表中 90种元素的电负性新标度。χ=0 .41 2 3 -EV,该式表明电负性值与价键轨道能量的绝对值的平方根成正比 ,所得数值是一套无量纲的相对参数。元素电负性值随价态的升高与元素非金属性的增强相对应 ,元素电负性的大小不仅与单个成键电子有关 ,而且也与参加价键作用的多个电子甚至整个价层都有紧密的联系。氢的元素电负性值不同于Pauling值、等于 1 .52。用 1 6种氢化物中键的额外离子能Δ′对 (χA-χB) 2 作图 ,两者之间确实具有良好的线性关系。本方法充分体现了目前公认的三大电负性标度的优点 ,该标度同时也是价层电子在价键状态下的一种能量标度 ,是对元素周期律的定量描述和反映。     

Experimental and Theoretical Studies of the HeICl Van der Waals Complexes in the Valence and Ion-pair States

The article presents results of experimental and theoretical analysis of the T-shaped and linear HeICl van der Waals complexes in the valence A1 and ion-pair β1 states as well as the HeICl(A1,v_A,n_A←X0⁺,v_X=0,n_x and β1,v_β,n_β←A1,v_A,n_A) optical transitions (n_i are quantum numbers of the vdW) modes). The HeICl(β1,v_β,n_β)→He+ICl(E0⁺, , β1) decay are also studied. Luminescence spectra of the HeICl(β1,v_β=0–3,n_β) complex electronic (ICl(E0⁺,v_E, ) and vibrational ICl(β1,v_β) predissociation products are measured, and branching ratios of decay channels are determined. To construct potential energy surfaces for the HeICl(A1, β1) states, we utilized the intermolecular diatomic-in-molecule perturbation theory first order method. Experimental and calculated spectroscopic characteristics of the A1 and β1 states agree well. Comparison of the experimental and calculated pump-probe, action and excitation spectra shows that the calculated spectra describe the experimental spectra adequately.     

碳原子价轨道电负性对化学键性能的影响

研究了同一类型化学键X―C的键能、键长和H―C键的酸性等性能与碳原子价轨道电负性的定量关系。结果表明,X―C键能随碳原子价轨道电负性增加而线性增大;H―C与C―C键的键长随碳原子价轨道电负性增加而线性减小;H―C的酸性随碳原子价轨道电负性增加而线性增大。因而,对结构类似的有机化合物,可以采用碳原子价轨道电负性对实验测定的化学键性能作图,判断其测定结果正确与否。     

A Valence Bond Study of the Low‐Lying States of the NF Molecule

The electronic structures of the three lowest‐lying states of NF are investigated by means of modern valence bond (VB) methods such as the VB self‐consistent field (VBSCF), breathing orbital VB (BOVB), and VB configuration interaction (VBCI) methods. The wave functions for the three states are expressed in terms of 9–12 VB structures, which can be further condensed into three or four classical Lewis structures, whose weights are quantitatively estimated. Despite the compactness of the wave functions, the BOVB and VBCI methods reproduce the spectroscopic properties and dipole moments of the three states well, in good agreement with previous computational studies and experimental values. By analogy to the isoelectronic O₂ molecule, the ground state ³Σ^? possesses both a σ bond and 3‐electron π bonds. However, here the polar σ bond contributes the most to the overall bonding. It is augmented by a fractional (19 %) contribution of three‐electron π bonding that arises from π charge transfer from fluorine to nitrogen. In the singlet ¹Δ and ¹Σ⁺ excited states the π‐bonding component is classically covalent, and it contributes 28 % and 37 % to the overall bonding picture for the two states, respectively. The resonance energies are calculated and reveal that π bonding contributes at least 24, 35 and 42 kcal mol^?1 to the total bonding energies of the ³Σ^?, ¹Δ and ¹Σ⁺ states, respectively. Some unusual properties of the NF molecule, like the equilibrium distance shortening and bonding energy increasing upon excitation, the counterintuitive values of the dipole moments and the reversal of the dipole moments as the bond is stretched, are interpreted in the light of the simple valence bond picture. The overall polarity of the molecule is very small in the ground state, and is opposite to the relative electronegativity of N vs F in the singlet excited states. The values of the dipole moments in the three states are quantitatively accounted for by the calculated weights of the VB structures.     

容量法测定氧化钒中的各种价态钒

用NaOH溶液处理样品，分离V（V）然后以Fe(Ⅱ）滴定测定之。定量加入过量的V（V）到上述残渣中并用H2SO4溶解，用Fe(Ⅱ）滴定，计算出V（Ⅱ），V（Ⅲ）的含量。V（Ⅳ）的测定是通过从总钒量中扣除V（Ⅱ）、V（Ⅲ）、V（Ⅴ）的含量得到。V（Ⅱ）、V（Ⅲ）和V（Ⅴ）的回收率均大于96％，其8次测定结果的相对标准偏差分别为：9．8％、0．4％、1．2％；本法快速、简便，在实际应用中效果良好。     

Solid-State Photochemistry—A Method of Generating Unusual Valence States

High-energy radiation can give rise to pairs of complementary defects in nonmetallic solids by the transfer of electrons between various types of atoms. These “color centers” which are generally paramagnetic, can usually be described as unusual valence states of an element. They are destroyed by heating and in most cases regenerated by renewed irradiation. In a heteropolar solid the formation of color centers usually leads to cancellation of point charges due to foreign ions of other valence or to vacancies. This is shown by the examples of kunzite, brazilianite, smoky quartz, and citrine; the most important methods for the structural elucidation of color centers are also described. Application of the principle of charge balance opens up possibilities for the production of unusual valence states, e.g. Al²⁺, F^2?, Fe⁴⁺, and O^?. Moreover, the type of the color center often permits far-reaching conclusions to be drawn about the defect structure of real crystals, which could hardly be clarified in other ways.     

分子中含价层孤对电子的原子构型的判断方法

依据杂化轨道理论、价层电子对互斥理论、离域π键和实例,总结出了分子中含价层孤对电子原子构型的判断法,其内容为含有2对或3对孤对电子的原子(如F)可以存在sp1、sp2、sp3 3种杂化,若其相连的中心原子为sp1杂化,则该原子也为sp1杂化(如HC≡CF);若其相连的中心原子为sp2杂化,则该原子也为sp2杂化(如H2C＝CHF);若其相连的中心原子为sp3杂化,则该原子也为sp3杂化(如CH3F)。含有1对孤对电子的原子(如N)可以存在sp2、sp3 2种杂化,若其相连的中心原子为sp1或sp2杂化,则该原子均为sp2杂化(如HC≡CNH2和H2C＝CHNH2);若其相连的中心原子为sp3杂化,则该原子为sp3杂化(如CH3NH2)。并讨论了该方法的适用范围以及举例说明了该方法的应用。     

Average inner and outer radii in singly-excited 1<Emphasis Type="Italic">snl</Emphasis> states of the He atom

Average inner < r _< > and outer < r _> > radii are studied for 28 singly-excited 1 snl singlet and triplet states (0 ≤ l ≤ n ≤ 5) of the He atom. In all the cases, the average inner radius < r _< > is close to 0.75 bohr, which indicates that one of the two electrons behaves like the 1s electron in He⁺. On the other hand, an analysis of the average outer radius < r _> > shows that the other electron of the 1snl states behaves approximately like an snl electron in the hydrogen atom. The average outer radius < r _> > reflects more diffuse character of the singlet electron distribution. This paper is dedicated to the late Professor Serafin Fraga for his great contribution to quantum sciences. Contribution to the Serafin Fraga Memorial Issue.