二原子分子和三原子分子的周期表

门捷列夫元素周期表是自然科学中最重要的原则之一．然而，对于分子而言，却缺乏类似的表格．本文提出两个分别对应于二原子分子和三原子分子的周期表．这些分子周期表的格式和门捷列夫原子周期表相似．在这些表格中，分子依照它们各自的族数G和周期数P分类排列，G是价电子的数目而P则表示分子的尺寸．分子的基本性质，包括键长、结合能、力常数、电离势、自旋多重度、化学反应活性以及键角等等，都随着表中的G和P作周期性的变化．二原子分子和三原子分子的周期性因而被揭示开来．本文还进一步指出这种周期性是源出于分子的壳状电子构型．周期表中不仅包含了游离的分子，还包含了多原子分子中的“赝”分子．这些周期表可用来从本质上分类分子，广泛地预言分子的未知性质，了解在多原子分子中赝分子的作用，以及开拓新的研究领域，如芳香族、团簇或纳米微粒的周期性等．因此这些表格不仅能够引起多学科领域中科学工作者的关注，而且还能引起理科学生们的兴趣．

Periodic tables of diatomic and triatomic molecules

The Mendeleev periodic table of atoms is one of the most important principles in natural science. However, there is shortage of analog for molecules. Here we propose two periodic tables, one for diatomic molecules and one for triatomic molecules. The form of the molecular periodic tables is analogous to that of Mendeleev periodic table of atoms. In the table, molecules are classified and arranged by their group number G, which is the number of valence electrons, and the periodic number P, which represents the size of the molecules. The basic molecular properties, including bond length, binding energy, force constant, ionization potential, spin multiplicity, chemical reactivity, and bond angle, change periodically within the tables. The periodicities of diatomic and triatomic molecules are thus revealed. We also demonstrate that the periodicity originates from the shell-like electronic configurations of the molecules. The periodic tables not only contain free molecules, but also the ＂virtual＂ molecules present in polyatomic molecules. The periodic tables can be used to classify molecules, to predict unknown molecular properties, to understand the role of virtual molecules in polyatomic molecules, and to initiate new research fields, such as the periodicities of aromatic species, clusters, or nanoparticles. The tables should be of interest not only to scientists in a variety of disciplines, but also to undergraduates studying natural sciences.