◆ Basis: Arrange elements with similar chemical properties in the same vertical row according to the relative atomic mass from small to large.

◆ Significance: It reveals the internal relationship between chemical elements and becomes one of the important milestones in the history of chemical development.

Development: With the development of science, the vacancies left by unknown elements in the periodic table have been filled one after another.

Symbol, * * * is divided into five areas:

Zone S: It includes family IA, family IIA and family Helium, and its valence electron configuration is NS 1 ~ 2.

Area P: including IIIA, IVA, VA, VIA, VIIA and 0 (except helium). The valence electron configuration is NS2NP 1 ~ 6.

Zone D: It includes elements from IIIB to VIII except lanthanides and actinides, and its valence electron configuration is (n-1) d1~ 9 ns1~ 2.

Ds region: including IB and IIB, with valence electron configuration of (n-1) d10ns1~ 2.

Zone F: It includes lanthanides and actinides, and its valence electron configuration is (n-2) f0 ~14 (n-1) d0 ~ 2ns2.

Ds region: including subfamily 1 and 2, with valence electron configuration of (n-1) d10ns1-2.

Zone F: It includes lanthanides and actinides, and its valence electron configuration is (n-2) f0-14 (n-1) d0-2ns2.