The periodic table of chemical elements is a list of chemical elements sorted from small to large according to the charge number of nuclear power. The list is generally rectangular, and some elements have spaces in their periods, so that elements with similar characteristics belong to the same group, such as alkali metal elements, alkaline earth metals, halogen elements, rare gases, nonmetals and transition elements.
This makes the periodic table of elements divided into 7 main groups, 7 sub-groups, 8 groups and 0 groups. Because the periodic table of elements can accurately predict the characteristics of various elements and their relationships, it is widely used in chemistry and other scientific fields as a very useful framework for analyzing chemical behavior.
Extended data:
Except 1 period, the valence of elements increases from left to right in the same period. In the second cycle, the highest positive valence of elements increased from alkali metal+1 to nitrogen element +5 (fluorine has no positive valence and oxygen has no highest positive valence), the highest positive valence of other periodic elements increased from alkali metal+1 to +7, and the negative valence of nonmetallic elements increased from carbon group -4 to -655. The highest positive valence and the lowest negative valence of the elements of the same main group are the same.
Melting point of simple substance, with the increase of atomic number of elements in the same period, the melting point of metallic simple substance composed of elements increases, while the melting point of nonmetallic simple substance decreases; (The melting point of subgroup reached the highest in VIB group, and then decreased in turn. ) From top to bottom, the melting point of metallic elements in the same group decreases, while the melting point of nonmetallic elements increases. (informal sub-tribe)