The pattern of elements in the periodic table reflects the progressive filling of electronic orbitals. The two columns on the left—the alkali metals and alkaline earths—show the addition of 1 and 2 electrons into s‐type subshells. (See Figure 1.)
Figure 1. Filling of the s subshells.
The loss of these s‐subshell valence electrons explains the common +1 and +2 charges on ions of these elements, except for helium, which is chemically inert.
The six elements from boron through neon show the insertion of electrons into the lowest energy p‐type subshell. (See Figure 2.)
Figure 2. Filling of the 2 p subshell.