化学专业英语翻译(修订版)02非金属元素.doc

化学专业英语 翻译（校准版） 02 THE NONMETAL ELEMENTS 02非金属元素 We noted earlier. that -nonmetals exhibit properties that are greatly different from those of the metals. As a rule, the nonmetals are poor conductors of electricity (graphitic carbon is an exception) and heat; they are brittle, are often intensely colored, and show an unusually wide range of melting and boiling points. Their molecular structures, usually involving ordinary covalent bonds, vary from the simple diatomic molecules of H2, Cl2, I2, and N2 to the giant molecules of diamond, silicon and boron. 我们早知道非金属表现出来的性质是和金属大不相同的。一般来说，非金属是电与热的不良导体，石墨例外；他们是易碎的，通常呈现深颜色，并表现出异常广泛的熔点和沸点。他们的分子结构通常涉及到共价键的变化，包括简单的双原子分子氢气、氯气、碘和氮气，和巨大的金刚石、硅和硼。 The nonmetals that are gases at room temperature are the low-molecular weight diatomic molecules and the noble gases that exert very small intermolecular forces. As the molecular weight increases, we encounter a liquid (Br2) and a solid (I2) whose vapor pressures also indicate small intermolecular forces. Certain properties of a few nonmetals are listed in Table 2. 在室温下，低分子量的双原子分子的气态非金属和惰性气体相遇会产生非常小的分子间作用力。随着分子量的增大，我们知道液体（Br2）和固体（碘）的蒸汽压也表现出较小的分子间作用力。一些非金属的某些性质列在表2中。 Simple diatomic molecules are not formed by the heavier members of Groups V and VI at ordinary conditions. This is in direct contrast to the first members of these groups, N2 and O2. The difference arises because of the lower stability of π bonds formed from p orbitals of the third and higher main energy levels as opposed to the second main energy level2. The larger atomic radii and more dense electron clouds of elements of the third period and higher do not allow good parallel overlap of p orbitals necessary for a strong π bond. This is a general phenomenon — strong π bonds are formed only between elements of the second period. Thus, elemental nitrogen and oxygen form stable molecules with both σ and π bonds, but other members of their groups form more stable structures based on σ bonds only at ordinary conditions. Not