D-block

The d-block is the portion of the periodic table that contains the element groups 3–12. These groups correspond to the filling of the atomic d-orbital subshell of the second outermost shell (inside an outermost shell only containing 1 or 2 s-orbital electrons) with electron configurations ranging from s2d1 (Group 3) to s2d10 (Group 12). There are some irregularities in the sequence; for example Cr is s1d5 (not s2d4) and the Group 11 metals are s1d10 (not s2d9), so that the d-subshell is actually complete at Group 11.