A stable configuration is a completely filled
s‐type subshell and a
p‐type subshell. Only five elements have atoms with their valence
p‐subshells filled; these are the inert gases in the far right column of the periodic table. Their lack of chemical reactivity is explained by their stable electron configurations.
All other chemical elements need to lose or gain electrons to achieve electronic stability. Table 1 shows the stable electron configurations for the elements in the first three rows of the periodic table.
Most atoms achieve a stable number of valence electrons by sharing electrons with other atoms. Begin with fluorine, element 9, which has the electron configuration 1 s 2 2 s 2 2 p 5. The orbitals of the valance electron shell are 2 s 2 p, with two electrons in the 2 s and five electrons in the 2 p. These seven valence electrons can be portrayed in a diagram devised by the American chemist Gilbert Lewis (1875–1946). In Figure 1, a Lewis diagram shows each valence electron as a single dot.
Figure 1. The valence electrons.