对改进的价层电子对互斥模型的几点修正与补充

价层电子对互斥理论(简称VSEPR理论)是判断简单共价键分子几何构型的一种简便方法。这一理论最初由西基威克(N.V.Sidgwick)和鲍威尔(H.M.Powell)于1940年提出,后经吉莱斯皮(R.J.Gillespie)和尼荷姆(R.S.Nyholm)加以改进、发展而得到普及。目前,这一理论已普遍为一般教科书所引用。     

外层电子总数与价层电子对数的关系——介绍一种快速判断分子几何形状的方法

本文在价层电子对互斥理论的基础上,以八隅律为根据,提出了一种根据分子中外层电子数之和来求算中心原子的价层电子对数,从而推出分子几何形状的方法。克服了VSEPR法求算价层电子对数目的不足。     

ABn,ABnEm型分子或离子空间几何构型的预测

分子的空间几何构型是影响分子性质的重要因素。如何预测分子的空间几何构型,目前常用的理论主要是杂化轨道理论和价层电子对互斥理论(VSEPR理论),相对而言,VSEPR理     

价层电子对互斥理论

化学物质的许多物理性质和化学性质都与原子在分子中的相对位置有密切关系。因此,研究分子的几何形状并找出其内在规律是很有意义的。在有关分子几何形状的定性理论中,定域电子对理论从六十年代以来发展很快,由 R.J.Gillespie 提出的价层电子对互斥理论(简称 VSEPR 理论)就是其中比较成功的一种模型。定域电子对理论的一个共同特点是假设泡利效应和静电效应使电子在分子的某些空间区域里有最大的出现几率,分子的几何形状和这些区域的关系十分密     

价层电子对互斥理论教学中几个问题的讨论

针对大学课程中价层电子对互斥（VSEPR）理论教学过程中存在的问题,对VSEPR理论的理论基础、过渡金属不适用于VSEPR理论的原因以及与杂化轨道理论之间的关系进行了讨论,并提出了教学建议。     

关于气态重碱土金属化合物单体折线构型的探究

针对无机化学中气态重碱土金属卤化物单体的折线构型进行讨论,解释其构型不符合价层电子对互斥理论(VSEPR)的原因,进一步总结影响分子构型的因素,并在此基础上提出相应的教学建议。     

价层电子对互斥理论中两个问题的讨论

针对大学化学课程中价层电子对互斥（VSEPR）理论教学过程中存在的问题，介绍和讨论VSEPR理论对于含有多重键分子构型的应用和AL，分子构型的特殊性质，并在此基础上提出了相应的教学建议。     

对使用价层电子对互斥模型的一个改进

价层电子对互斥模型(简称VSEPR模型)提供了判断AX_n型分子或离子几何构型的定性依据,但目前国内外流行的教科书及许多论述多以写出路易斯电子结构式作为使用此模型的前提。作者在教学中引进A.F.Wells所介绍的8_n+2m规则,可不需要写出路易斯电子结构式,而使模型的使用更为简便可靠。     

VSEPR模型的物理基础

目前用来解释和预测分子的几何构型的模型很多,如价层电子对排斥模型(VSEPR模型)、Walsh规则、三中心键模型、杂化理论等。由于不同的作者,在试图关联电子和分子结构时所采用的观点存在着很大的差异,因此,每个方法都有其一定的优点,     

探讨价层电子对互斥理论的电子对数计算简易方法与应用

针对价层电子对互斥理论中关于卤素、氧族等p区非金属元素作为配位原子提供电子数为1、0等未做明确说明的问题,通过数学公式推导解释了数字背后的意义,完善了将中心原子和配位原子按不同计算规则、更简便地计算价层电子对数的方法。应用推导出的简便价层电子对计算规则探讨了一种判断链状结构有机小分子的杂化类型的新方法,并讨论了长周期p区非金属元素的最外层s电子的钻穿作用对价层电子总数的影响以及利用电负性差异比较共价型分子键角大小时需要考虑多重键的影响等,对VSEPR法的应用做了有益补充。     

Electron Domains and the VSEPR Model of Molecular Geometry

The valence shell electron pair repulsion (VSEPR) model—also known as the Gillespie–Nyholm rules—has for many years provided a useful basis for understanding and rationalizing molecular geometry, and because of its simplicity it has gained widespread acceptance as a pedagogical tool. In its original formulation the model was based on the concept that the valence shell electron pairs behave as if they repel each other and thus keep as far apart as possible. But in recent years more emphasis has been placed on the space occupied by a valence shell electron pair, called the domain of the electron pair, and on the relative sizes and shapes of these domains. This reformulated version of the model is simpler to apply, and it shows more clearly that the Pauli principle provides the physical basis of the model. Moreover, Bader and his co-workers' analysis of the electron density distribution of many covalent molecules have shown that the local concentrations of electron density (charge concentrations) in the valence shells of the atoms in a molecule have the same relative locations and sizes as have been assumed for the electron pair domains in the VSEPR model, thus providing further support for the model. This increased understanding of the model has inspired efforts to examine the electron density distribution in molecules that have long been regarded as exceptions to the VSEPR model to try to understand these exceptions better. This work has shown that it is often important to consider not only the relative locations and sizes, but also the shapes, of both bonding and lone pair domains in accounting for the details of molecular geometry. It has also been shown that a basic assumption of the VSEPR model, namely that the core of an atom underlying its valence shell is spherical and has no influence on the geometry of a molecule, is normally valid for the nonmetals but often not valid for the metals, including the transition metals. The cores of polarizable metal atoms may be nonspherical because they include nonbonding electrons or because they are distorted by the ligands, and these nonspherical cores may have an important influence on the geometry of a molecule.     

New method for qualitative quantum chemical deductions on organic or inorganic molecules or clusters directly from structural formulas or ORTEP diagrams

A pictorial blackboard mnemonic type method presented allows the molecular orbital level patterns, the numbers of non-bonding, bonding, and anti-bonding orbitals to be figured out from the actual or tentative structural formulas (or ORTEP diagrams) of saturated or unsaturated molecules or intermediates regardless of symmetry. The simple pictorial rules are illustrated on: bicyclo[p.q.0] hydrocarbons, pyridine, alkyl groups, quaternium ions, some amines, ethers, water and alcohols, and on some fluorohydrocarbons. The readily obtained MO level patterns, e.g. during rearrangements, give a handle on the qualitative behaviour of various structures or species. The method applies also to metal atom and other clusters.List of abbreviations AO Atomic orbital - ECI Electron count index - H.F. Hartree-Fock - LPI Level pattern indices - MO Molecular orbital - SC Structurally covariant - SCF Self-consistent field - SEF Structural-electronic formula - SF Structural formula - VB Valence-bond - VIF Valency points interaction formula - VP Valency point - VL VP-VP' interaction line - VSEPR Valence shell electron pair repulsion     

Valence-Shell Electron-Pair Repulsion Theory Revisited: An Explanation for Core Polarization

Valence-shell electron-pair repulsion (VSEPR) theory constitutes one of the pillars of theoretical predictive chemistry. It was proposed even before the advent of the concept of “spin”, and it is still a very useful tool in chemistry. In this article we propose an extension of VSEPR theory to understand the core structure and predict core polarization in the main-group elements. We show from first principles (Electron Localization Function analysis) how the inner- and outer-core shells are organized. In particular, electrons in these regions are structured following the shape of the dual polyhedron of the valence shell (3^rd period) or the equivalent polyhedron (4^th and 5^th periods). We interpret these results in terms of “hard” and “soft” core character. All the studied systems follow this trend, providing a framework for predicting electron distribution in the core. We also show that lone pairs behave as “standard ligands” in terms of core polarization. The predictive character of the model was tested by proposing the core polarization in different systems not included in the original set (such as XeF₄ and [Fe(CN)₆]³⁻) and checking the hypothesis by means of a posteriori calculations. From the experimental point of view, the extension of VSEPR to the core region has consequences for current crystallography research. In particular, it explains the core polarization revealed by high resolution X-ray experiments.     

Models of molecular geometry

Although the structure of almost any molecule can now be obtained by ab initio calculations chemists still look for simple answers to the question "What determines the geometry of a given molecule?" For this purpose they make use of various models such as the VSEPR model and qualitative quantum mechanical models such as those based on the valence bond theory. The present state of such models, and the support for them provided by recently developed methods for analyzing calculated electron densities, are reviewed and discussed in this tutorial review.     

Is VSEPR valid?

Summary A chief tenet of VSEPR (valence shell electron pair repulsion theory) is that very electronegative atoms or groups attached to a central atom pull electrons toward themselves. These electron pairs, being farther apart, exert less repulsion, and consequently the bond angles involving them are decreased. A comparison of 37 pairs of common compounds shows that this rule holds only for hydrogen compounds. For other molecules, the size of the attached groups determines the bond angles.

---

VSEPR: ist es stichhaltig?

Zusammenfassung Ein Hauptgrundsatz der VSEPR (Valenzschalen-Elektronenpaar-Repulsion) Theorie heißt: hoch elektronegative, an einem Zentralatom angelagerte Atome oder Atomgruppen ziehen Elektronen an. Da sie weiter voneinander entfernt sind, üben diese Elektronenpaare weniger Repulsion aus. Daher werden die dazugehörigen Bindungswinkel vermindert. Ein Vergleich von 37 Paaren einfacher Verbindungen zeigt, daß diese Regel nur für Wasserstoffverbindungen gilt. In anderen Molekülen bestimmt die Größe der angelagerten Gruppen die Valenzwinkel.

     

How hydrides misled chemists

Hydrogen-containing molecules are simple enough to be attractive subjects in experimental diffraction and spectroscopic studies and in quantum computations. Yet, the inferences about molecular structure and force fields originally drawn from studies of these subjects were significantly flawed. In recent developments the original models of structure invoked, such as hybridization, have been superseded. The reasons for this are briefly reviewed. What has emerged to account for molecular geometry, prevailing even over the popular VSEPR theory, is a model of geminal nonbonded interactions.     

The Physical Basis of the VSEPR Model

The VSEPR model is a consequence of the correlation of same-spin electrons resulting from the operation of the Pauli exclusion principle. Although the VSEPR rules can be interpreted in terms of an orbital model they do not provide the physical basis for the model.     

高中化学新教材中VSEPR模型的b值规定之刍议

新教材关于VSEPR模型中b值的计算,暂未考虑"与中心原子结合的原子"所处的位置环境,即只做了静态规定,是符合新课标要求的;但若拓展运用在CH3COOH这样常见的分子上,会出现与常识不相符的情况,使得VSEPR模型的适用范围受限.从拓展高中化学的教与学的角度出发,笔者认为,将"与中心原子结合的原子"所处的位置环境考虑在...