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  • General

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  • 极极分子

    Ultracold polar molecules with phases and potential applications in quantum technology.

    How cold are ultracold polar molecules?
    ::极端冷极分子有多冷?

    Ultracold polar molecules have been created by scientists.  These “molecules” consists of Rb and K atoms excited by lasers to form a type of Rb-K where the Rb has a positive charge and the K has a negative charge.  The material is formed at temperatures extremely close to absolute zero . The researchers believe these techniques will help them make new reactions and new materials.
    ::极端极分子是由科学家创造的,这些“分子”由激光振动的Rb和K原子组成,形成一种Rb-K,Rb具有正电荷,K具有负电荷。材料在极接近绝对零的温度下形成。研究人员相信这些技术会帮助他们产生新的反应和新材料。

    Polar Molecules
    ::极极分子

    A polar molecule is a molecule in which one end of the molecule is slightly positive, while the other end is slightly negative.  An example of a diatomic molecule that consists of a polar covalent bond is hydrogen fluoride (HF).  In hydrogen fluoride, the hydrogen has a positive partial charge and the fluorine has a negative partial charge.  The two electrically charged regions on either end of the molecule are called poles, similar to a magnet having a north and a south pole.  A polar molecule is called a  dipole  because it has two poles. Similarly, a polar bond itself can be called a dipole. A dipole is indicated by an arrow  that starts on the positive end of the molecule and point s to the  negative end (see Figure ) .   

    ::极分子是一种分子,分子的一端略微呈正数,而另一端则略微呈负数。由极共价联结组成的二原子分子的一个例子是氟化氢(HFF);在氟化氢中,氢有正部分充电,氟化氢有负部分充电。分子两端的两个电充电区被称为极,类似于具有北极和南极的磁铁。极分子被称为二极分子,因为它有两极。同样,极联结本身也可以称为二极联结物。从分子正端开始的箭头显示二极联结物,点到负端(见图 ) 。

    Diagram illustrating polar molecule dipoles with positive and negative charges labeled.

    A dipole is any molecule with a positive end and a negative end, resulting from unequal distribution of electron density throughout the molecule.
    ::dipole系指由于整个分子的电子密度分布不均而产生正端和负端的任何分子。

    Polar molecules orient themselves in the presence of an electric field with the positive ends of the molecules being attracted to the negative plate while the negative ends of the molecules are attracted to the positive plate (see Figure ).
    ::极分子在电场出现时,将分子的正端吸引到负盘上,而分子的负端则吸引到正盘上(见图 )。

    Comparison of polar molecule orientation in electric field versus random orientation without field.

    Polar molecules are randomly oriented in the absence of an applied electric field (top). In an electric field, the molecules orient themselves because of the attraction of opposite charges (bottom).
    ::极分子在没有应用电场(顶部)的情况下随机调整方向。 在电场中,分子会因反向电荷的吸引而自我定向(底部)。

    For molecules with more than two atoms, the molecular geometry must also be taken into account when determining if the molecule is polar or nonpolar.  The Figure shows a comparison between carbon dioxide and water.  Carbon dioxide (CO 2 ) is a linear molecule.  The oxygen atoms are more electronegative than the carbon , so there are two individual dipoles pointing outward from the C atom to each O atom.  However, since the dipoles are of equal strength and are oriented in this way, they cancel each other out and the overall molecular of CO 2 is zero.
    ::对于两个以上原子的分子,在确定分子是极分子还是非极分子时,也必须考虑到分子几何。图中显示了二氧化碳和水之间的比较。二氧化碳(CO2)是一个线性分子。氧原子比碳更具有电阴性,因此从C原子到每个O原子,有两颗单极极。然而,由于底极的强度相等,并且以这种方式定向,它们相互抵消,二氧化碳的总分子为零。

    Water is a bent molecule because of the two lone pairs on the central oxygen atom.  The individual dipoles point from the H atoms toward the O atom.  Because of the shape, the dipoles do not cancel each other out and the water molecule is polar.  In the Figure , the net dipole is shown in blue and points upward.
    ::水是一个弯曲分子, 原因是中央氧原子上的两个单对。 从H原子到O原子, 单个的顶点。 由于形状, 顶点不会相互抵消, 而水分子是极的。 图中, 净底点以蓝色显示, 向上点显示 。

    Comparison of molecular dipoles in CO2 (nonpolar) and H2O (polar) with dipole orientation.

    The molecular geometry of a molecule affects its polarity.
    ::分子的分子几何学影响其极性。

    Some other molecules are shown in the Figure .  Notice that a tetrahedral molecule such as CH 4 is nonpolar.  However, if one of the peripheral H atoms is replaced with another atom that has a different electronegativity , the molecule becomes polar.  A trigonal planar molecule (BF 3 ) may be nonpolar if all three peripheral atoms are the same, but a trigonal pyramidal molecule (NH 3 ) is polar.
    ::图中显示了其他一些分子。请注意,象CH4这样的四面分子是非极性分子。然而,如果将一个外围H原子替换为另一个具有不同电子强度的原子,分子就会变成极性。如果所有三个边缘原子都相同,而三角金字塔分子(NH3)是极性,则三角平面分子(BF3)可能是非极性分子。

    Examples of polar and nonpolar molecules showcasing diverse molecular geometries.

    Some examples of polar and nonpolar molecules based on molecular geometry.
    ::一些以分子几何学为基础的极分子和非极分子的例子。

     

     

    Why does water form droplets? How does soap get our clothes clean? Hint: both actions have to do with polarity. Try these simulations to learn more: 
    ::为何水状滴子? 肥皂如何让我们的衣服干净? 提示: 两种行动都与极性有关。 尝试这些模拟来学习更多:

    Summary
    ::摘要

    • Polar molecules result from differences in electronegativity of the atoms in the molecule.
      ::极分子是分子原子电子密度差异的结果。
    • Dipoles that are directly opposite one another cancel each other out.
      ::直接对立的对立极互相抵消

    Review
    ::回顾

    1. Why is a polar molecule called a dipole?
      ::为什么一个极分子叫做?
    2. The molecular geometry of NH 3 is trigonal pyramidal. What about the molecular geometry of NH 3 makes it a polar molecule?
      ::NH3的分子几何是三角金字塔。 NH3的分子几何如何使它变成极分子?
    3. What happens to polar molecules when an electric field is applied?
      ::当应用电场时,极分子会怎么样?