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  • General

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  • VSEPR 理论

    Comparison of water (H2O) and carbon dioxide (CO2) molecular shapes and angles.

    Why is the water molecule bent like that?
    ::为什么水分子会这样弯曲?

    The characteristic bent shape of the water molecule shown above was a puzzling discovery for scientists at first. The shape allows the molecule to be polar, increasing its boiling point and making it possible for life on earth to exist as we know it. But what makes it bend? The structure is almost the same as carbon dioxide which is known to be a at room temperature , why not water too?
    ::上面显示的水分子的弯曲形状最初对科学家来说是一个令人费解的发现。 这个形状让分子成为极极,增加其沸点,并使我们所知道的地球上的生命得以存在。但是什么使它弯曲?结构几乎和二氧化碳一样,而二氧化碳在室温下是已知的,为什么水也不会存在呢?

    Putting atoms together to form compounds can be done on paper or in the lab.  However, when the shape of the molecule made in the lab is different from the shape of the molecule drawn on paper, then we need to rethink our ideas and find better explanations.
    ::将原子组合成化合物可以在纸上或实验室中完成。 但是,当实验室制造的分子形状与纸上提取的分子形状不同时,我们需要重新思考我们的想法,找到更好的解释。

    VSEPR Theory
    ::VSEPR 理论

    In 1956, British scientists R.J. Gillespie and R.S. Nyholm recognized that the current model for explaining bond angles did not work well.  The theory at that time relied on hybrid orbitals to explain all aspects of bonding.  The problem was that the theory gave incorrect prediction of bond angles for many compounds.  They developed a new approach based on earlier work by other scientists that incorporated a consideration of pairs in predicting three-dimensional structure.
    ::1956年,英国科学家吉莱斯皮和尼霍尔姆认识到,目前解释债券角度的模式不起作用,当时的理论依靠混合轨道来解释联结的所有方面,问题是理论错误地预测了许多化合物的债券角度,他们根据其他科学家早先的工作制定了一种新方法,在预测三维结构时考虑到对子。

    The valence shell is the outermost electron-occupied shell of an .  The valence shell holds the electrons that are involved in bonding and are the electrons shown in a Lewis structure.  The acronym VSEPR stands for the valence-shell electron pair repulsion model.  The model states that electron pairs will repel each other such that the shape of the molecule will adjust so that the valence electron-pairs stay as far apart from each other as possible. Molecules can be systematically classified according to the number of bonding pairs of electrons as well as the number of nonbonding or lone pairs around the central atom. For the purposes of the VSEPR model, a double or triple bond is no different in terms of repulsion than a single bond.
    ::valence shell 是一个最外层电子占用的外壳。 valence shell shell 包住连接中所涉及的电子, 是显示在 Lewis 结构中的电子 。 缩略语 VSEPR 代表着valence- shell 电子对式击退模型 。 该模型指出, 电子对子将互相击退, 使分子的形状能够调整, 使valence econ- pair 尽可能地保持距离 。 molecules 可以按照电子连接对子的数量以及中央原子周围的非捆绑或独一对子的数量进行系统分类 。 为了 VSEPR 模型的目的, 双倍或三倍的连接在击退方面与单一的连接没有区别 。

     

     

     

     

    Summary
    ::摘要

    • VSEPR theory allows more accurate predictions of molecular shape.
      ::VSEPR理论使得能够更准确地预测分子形状。

    Review
    ::回顾

    1. Who did the major work in developing the VSEPR theory?
      ::谁是发展VSERPR理论的主要工作者?
    2. Where are the electrons that are involved in bonding?
      ::连接所涉及的电子在哪里?
    3. What is the basic idea behind the VSEPR theory?
      ::VSERPR理论背后的基本理念是什么?