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  • General

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  • 物理属性和中分子力

    A display featuring a diamond necklace, highlighting its value and properties in chemistry.


    Can you guess how much this is worth?
    ::你能猜到这值多少钱吗?

    Carbon is an interesting and versatile . There are over twenty million known compounds containing carbon, encompassed in the growing field of organic chemistry . The element itself can exist in two major forms. Diamond is a form of carbon that is extremely hard and is one of the few materials that can scratch glass. The other form of carbon is graphite, a very soft material that we find in “lead” pencils. The two forms differ mainly in how the carbon atoms are connected to one another. The differences in the arrangement of atoms affect the properties of the material.
    ::碳是一种有趣和多用途的碳。有2 000多万种已知的碳化合物,包含在有机化学的不断增长的领域。元素本身可以以两种主要形式存在。钻石是一种极其硬的碳形式,是能够刮碎玻璃的少数材料之一。另一种碳形式是石墨,这是我们在“铅”铅笔中找到的非常软的材料。两种形式在碳原子相互连接的方式上大不相同。原子的配置差异影响材料的特性。

    Physical Properties and Intermolecular Forces
    ::物理属性和中分子力

    The physical state and properties of a particular depend in large part on the type of chemical bonding it displays. , sometimes called covalent compounds, display a wide range of due to the different types of intermolecular attractions such as different kinds of polar interactions. The and boiling points of molecular compounds are generally quite low compared to those of . This is because the energy required to disrupt the intermolecular forces between molecules is far less than the energy required to break the in a crystalline ionic compound. Since molecular compounds are composed of neutral molecules, their electrical conductivity is generally quite poor, whether in the solid or state. Ionic compounds do not conduct electricity in the solid state because of their rigid structure, but conduct well when either molten or dissolved into a solution. The water of molecular compounds is variable and depends primarily on the type of intermolecular forces involved. Substances that exhibit or dipole-dipole forces are generally water soluble, whereas those that exhibit only London dispersion forces are generally insoluble. Most, but not all, ionic compounds are quite soluble in water. Table summarizes some of the differences between ionic and molecular compounds.
    ::特定分子的物理状态和特性在很大程度上取决于其显示的化学结合类型。有时被称为共价化合物,由于不同种类的分子吸引,例如不同种类的极地相互作用,表现出了各种各样的不同种类的分子性吸引,例如不同种类的极地相互作用。一般而言,分子化合物的热点和沸点与分子的分子性能相比相当低。这是因为破坏分子之间分子的中间分子性能所需的能量远远低于打破晶状离子化合物所需的能量。由于分子性化合物由中性分子组成,它们的电导性一般相当差,无论是在固体还是状态。离子化合物由于结构僵硬,不进行固态的电力,但在熔化或溶解成溶解溶液时则进行良好。分子性化合物的水是可变的,主要取决于所涉分子性力量的类型。显示或二极作用的物质一般都是水溶解的,而仅显示伦敦的分散性力量一般是溶解的。大多数但并非全部的离子化合物在水中都是相当溶解的。

    Comparison of Ionic and Molecular Compounds
    Property Ionic Compounds Molecular Compounds
    Type of elements metal and nonmetals only
    Bonding ionic – transfer of electron(s) between atoms covalent – sharing of pair(s) of electrons between atoms
    Representative unit formula unit molecule
    Physical state at room temp. solid , liquid, or solid
    Water solubility usually high variable
    Melting and boiling temps generally high generally low
    Electrical conductivity good when molten or in solution poor

    One type of molecular compound behaves quite differently than that described so far. A covalent network solid is a compound in which all of the atoms are connected to one another by . Diamond is composed entirely of carbon atoms, each bonded to four other carbon atoms in a tetrahedral geometry. Melting a covalent network solid is not accomplished by overcoming the relatively weak intermolecular forces. Rather, all of the covalent bonds must be broken, a process that requires extremely high temperatures. Diamond, in fact, does not melt at all. Instead, it vaporizes to a gas at temperatures above 3500°C.
    ::一种类型的分子化合物的行为与目前描述的完全不同。一种共价网络固体是一种所有原子都由......连接在一起的化合物。钻石完全由碳原子组成,每个碳原子在四面形几何中联结为另外四个碳原子。一种共价网络的固体不能通过克服相对薄弱的中间分子力量来融化。相反,所有共价债券都必须打破,这一过程需要极高的温度。事实上,钻石根本不会融化。相反,它蒸发到温度在3500摄氏度以上的气体中。

     

     

    Summary
    ::摘要

    • The physical properties of a material are affected by the intermolecular forces holding the molecules together.
      ::材料的物理特性受到将分子放在一起的分子间联力量的影响。

    Review
    ::回顾

    1. Are melting points of molecular compounds generally higher or lower than those of ionic compounds?
      ::分子化合物的熔点一般高于或低于离子化合物的熔点吗?
    2. Do ionic compounds conduct electricity in the solid state?
      ::离子化合物在固体状态下进行电力供应?
    3. What types of substances are generally water-soluble?
      ::哪些物质一般可以溶解水?