应用氧化数的概念讨论马氏规则

在不对称烯烃加成反应中,马氏规则及反马氏规则都是非常熟悉的一个反应,但在反应机理的解释上却不尽一致,而应用氧化数的概念很容易统一马氏规则和反马氏规则. 1.氧化数概念对马氏规则的应用氧化数的概念是建立在经典的化合价学说和元素电负性的基础上,在一定程度上标志着元素在化合物中的化合状态.规定: (1)电负性相同的两个元素之间的结合,则这两个元素的氧化数为零.     

从“得失氧”到“极性翻转”:氧化还原反应概念的历史演变

18世纪末,拉瓦锡在氧化学说范式下,建立了“得失氧”角度上的氧化还原反应的概念。19世纪,约翰逊在化合价学说的基础上,发现氧化还原反应的共同特征是“化合价升降”,其概念扩大至反应前后化合价发生升降的一类反应。20世纪初,弗莱从“电子转移”的角度解释了化合价升降的原因,揭示了氧化还原反应的微观本质。1948年,格拉斯顿在价键理论和电负性基础上,从“氧化数变化”的角度提出了氧化还原反应的人为表征概念。20世纪末,古德斯坦和李良助分别从“电负性顺序”和“极性翻转”角度提出了氧化还原反应的现代理解。氧化还原反应概念的发展史,反映了化学思想的发展和科学认识的变化,对化学研究有重要的启示。     

外层电子总数与价层电子对数的关系：介绍一咱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遥方法。克服了ＶＳＥＰＲ法求算价层电子对数目的不足。     

复杂氧化还原滴定结果计算的总电子得失守恒法*

对于复杂氧化还原滴定结果的计算,从氧化还原反应的本质——电子得失入手,提出了总电子得失守恒法,并通过实例加以运用说明。具体步骤为:首先写出反应方程式,无需配平;然后找出整个反应过程前后氧化数发生改变的氧化剂和还原剂,并标注其氧化数;最后根据氧化剂得电子总数与还原剂失电子总数相等的原则列等式并带入数据计算。该方法简单易懂,无需配平反应方程式,可以缩短解题时间,减少出错概率,并有助于强化学生对氧化还原滴定的定量依据——总电子得失守恒的理解。     

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。     

化合价的历史演变

回顾了化合价概念的发展历史,其中包括化合价概念的提出、化学结构理论的创立、化合价的电子理论的发展、基于现代化学键理论的化合价规则等.介绍了区别化合价与氧化数的相关论述,以助于对化合价概念的理解.     

有机化学中的氧化和还原

本文概述了氧化数这个氧化还原最基本的概念,阐述了有机化合物氧化还原的本质是碳的氧化和还原,其结果是碳所形成的两类共价键产生了彼此转换,阐述了如何用电子得失的观点考察有机化合物的氧化还原,并介绍了形式电荷与氧化数在概念上的差别。     

价层电子对互斥理论的改进——计算中心原子价层电子对数的新方法

对氢、卤素、氧族元素作配位原子时提供的价电子数做了合理的解释，并推导出计算中心原子价层电子对数的新方法，该方法不需要书写路易斯结构式再确定成键电子对数和孤电子对数，也不必规定不同族的原子作配位原子时提供的价电子数，只需要根据公式即可直接得到中心原子的价层电子对数。     

碳还原数的概念和意义

作者认为,对氧化数的概念稍作调整,即可构成一个新的概念,不仅能定量标示有机物分子的还原态,而且是一个有用的生物能力学参数,姑且称之为碳还原数。一、联还原数的概念根据IUPAC对氧化数的定义,各种碳原子的氧化数如表1。氧化数虽也可用于比较不同有机分子的氧化态,但相加时正负数抵销,致使许多化合物的碳氧化数为0,如葡萄糖和乙酸均为0(图1)。欲扩大它的应用范围,必须设法消除负值。为此,作者建议以价     

中心原子价层电子对数目计算和分类

在一些普通化学教科书中价层电子对互斥理论关于中心原子价层电子对的数目计算存在不一致,也没有对中心原子的电子对进行系统分类。本文提出一种符合化合价原则但又不超越该理论基础的算法,并根据逻辑学中有关划分的规则按照电子对的不同属性对中心原子所有的电子对进行了系统分类,达到对中心原子电子对的全面认识,提出定构价层电子对概念并由其判断分子构型。显示逻辑学规则在化学教学中的重要作用。     

Subvalenz bei elektropositiven s‐Block‐Metallen. Unmögliches möglich gemacht

The preparation of subvalent electropositive metal compounds succeeds in general by means of three different concepts: i) Stabilization can be achieved by delocalization of electrons in metallic matrices. A formal subvalence results from the total formula, whereas on closer examination of the bonding situation an expected “normal” valence of the metal atoms according to the octet rule can be concluded. ii) According the rules of determination of the oxidation state a formal subvalence arises from the formation of homonuclear element‐element bonds or metal clusters. However, in the case of M₂²⁺ units a normal valence is realized (which is well‐known in the chemistry of mercury as Hg₂²⁺, e.g. calomel Hg₂Cl₂). iii) The stabilization of subvalent metals with the aid of expanded π*‐systems of aren ligands succeeds when the energy lies between the two first ionization energies of the alkaline earth metal.     

大学无机化学与高中化学知识衔接——以原子结构与元素周期表为例

原子结构理论是高中化学和大学无机化学的重要组成部分和学习难点,教学过程中如何较好地衔接高中阶段知识与大学无机化学课程尤为重要。本文以原子结构和元素周期表知识点为例,以2019版高中人教版教材和北师大版的无机化学教材内容讨论高中化学知识与大学化学知识的衔接问题,依据作者的教学实践提出若干建议,为大学无机化学原子结构与元素周期表知识点的教学提供参考,同时帮助大一学生顺利完成知识的衔接过渡和培养学生独立思考、自主学习的能力。     

The role of "external" lone pairs in the chemical bonding of bare post-transition element clusters: the Wade-Mingos rules versus the jellium model

The jellium sphere model of a volume of electrons, counterbalanced by a positive charge throughout the sphere, leads to an energy level sequence corresponding to special stabilities of bare post-transition element clusters with 20 valence electrons such as the known P4 and clusters with 40 valence electrons such as the known Ge9(4-), Ni@In10(10-), and In11(7-). In this model the otherwise "external" lone pairs on the vertex atoms participate at least indirectly in the skeletal bonding. Furthermore, this model predicts the most favorable polyhedra and electron counts in some cases to be quite different than those predicted by the Wade-Mingos rules of polyhedral borane chemistry.     

氧化数教学争议的化解

Starting with the definition of oxidation number and the development of its concept, the controversial issues in the teaching of oxidation number were discussed in this paper, and the rule that the positive oxidation number of the element should be less than or equal to the total numbers of valence electrons of the atom was put forward to determine the oxidation number. Additionally, the calculation of oxidation number in the compounds with complex structure and unknown structure has been resolved.     

原子簇与有关分子的结构规则(Ⅰ)-(nxcπ)格式

包括原子簇在内的无机和有机分子可认为由若干分子片所组成,它们的结构类型可由四个数(nxcπ)来规定。文中提出七条结构规则来阐明原子簇及有关分子的结构和成键能力,并举例说明这些结构规则和(nxcπ)格式的应用,如由分子式估算结构类型,预测新的原子簇化合物及其可能的合成途径等。     

Idiosyncratic Ag7Pt2O7: An Electron Imprecise yet Diamagnetic Small Band Gap Oxide

The seminal qualitative concepts of chemical bonding, as presented by Walter Kossel and Gilbert Newton Lewis back in 1916, have lasting general validity. These basic rules of chemical valence still serve as a touchstone for validating the plausibility of composition and constitution of a given chemical compound. We report on Ag₇Pt₂O₇, with a composition that violates the basic rules of chemical valence and an exotic crystal structure. The first coordination sphere of platinum is characteristic of tetravalent platinum. Thus, the electron count corresponds to Ag₇Pt₂O₇*e⁻, where excess electrons are associated with the silver substructure. Such conditions given, it is commonly assumed that the excess electrons are either itinerant or localized in Ag−Ag bonds. However, the material does not show metallic conductivity, nor does the structure feature Ag-Ag pairs. Instead, the excess electrons organize themselves in 2e−4c bonds within the silver substructure. This subvalent silver oxide reveals a new general facet pertinent to silver chemistry.     

Kβ X‐Ray Emission Spectroscopic Study of a Second‐Row Transition Metal (Mo) and Its Application to Nitrogenase‐Related Model Complexes

In recent years, X‐ray emission spectroscopy (XES) in the Kβ (3p‐1s) and valence‐to‐core (valence‐1s) regions has been increasingly used to study metal active sites in (bio)inorganic chemistry and catalysis, providing information about the metal spin state, oxidation state and the identity of coordinated ligands. However, to date this technique has been limited almost exclusively to first‐row transition metals. In this work, we present an extension of Kβ XES (in both the 4p‐1s and valence‐to‐1s [or VtC] regions) to the second transition row by performing a detailed experimental and theoretical analysis of the molybdenum emission lines. It is demonstrated in this work that Kβ₂ lines are dominated by spin state effects, while VtC XES of a 4d transition metal provides access to metal oxidation state and ligand identity. An extension of Mo Kβ XES to nitrogenase‐relevant model complexes shows that the method is sufficiently sensitive to act as a spectator probe for redox events that are localized at the Fe atoms. Mo VtC XES thus has promise for future applications to nitrogenase, as well as a range of other Mo‐containing biological cofactors. Further, the clear assignment of the origins of Mo VtC XES features opens up the possibility of applying this method to a wide range of second‐row transition metals, thus providing chemists with a site‐specific tool for the elucidation of 4d transition metal electronic structure.     

Inorganic ion-exchangers: Their role in chromatographic radionuclide generators for the decade 1993-2002

Ion-exchangers are found not only in water purification processes, the original major application, but also in analytical chemistry for the separation and isolation of elements, hydrometallurgy, inorganic chemistry and biochemistry, in food technology, and of course in many specialized fields related to the utilization of atomic energy. The use of organic ion-exchangers is limited by virtue of their limited stability under harsh conditions, whereas inorganic ion-exchangers possess important properties, which make them very useful for chemical separation and purification in intense radiation fields. The availability of short-lived radionuclides from radionuclide generators provides an inexpensive and convenient alternative to in-house radioisotope production facilities such as accelerators and cyclotrons. Due to their simplicity of operation, chromatographic based generators have been the method of choice, although generators based on solvent extraction and on volatization and sublimation have also been developed, and are routinely used. In this paper use of inorganic ion-exchangers for the development of radionuclide generators for the decade 1993–2002 has been compiled.     

Inorganic ion-exchangers: Their role in chromatographic radionuclide generators for the decade 1993–2002

Ion-exchangers are found not only in water purification processes, the original major application, but also in analytical chemistry for the separation and isolation of elements, hydrometallurgy, inorganic chemistry and biochemistry, in food technology, and of course in many specialized fields related to the utilization of atomic energy. The use of organic ion-exchangers is limited by virtue of their limited stability under harsh conditions, whereas inorganic ion-exchangers possess important properties, which make them very useful for chemical separation and purification in intense radiation fields. The availability of short-lived radionuclides from radionuclide generators provides an inexpensive and convenient alternative to in-house radioisotope production facilities such as accelerators and cyclotrons. Due to their simplicity of operation, chromatographic based generators have been the method of choice, although generators based on solvent extraction and on volatization and sublimation have also been developed, and are routinely used. In this paper use of inorganic ion-exchangers for the development of radionuclide generators for the decade 1993–2002 has been compiled.     

Solution redox chemistry of carbon nanotubes

UV/vis/NIR absorbance spectra were used to monitor electron transfer between small-molecule redox reagents and carbon nanotubes (CNTs). The oxidation of (6, 5)-enriched nanotubes in water with K(2)Ir(Cl)(6) reveals a valence electron density of 0.2-0.4 e(-)/100 carbon atoms and a reduction potential of approximately 800 mV versus NHE. The reduction potential of CNTs is found to increase with increasing band gap and to decrease with the introduction of an anionic dispersant. In light of this newly revealed redox chemistry of CNTs, we propose that the previously observed bleaching of the CNT absorbance spectrum at low pH is most likely a consequence of the oxidation of the nanotubes by oxygen. These results demonstrate facile oxidation and reduction of CNTs, provide a way to quantify the population of valence electrons, and point to possible applications of CNT in the catalysis of redox reactions.