1.0 General Introduction and Electronic Configuration

  d and f Block Elements

• The elements in which last electron is entering in $d$ orbital of the penultimate shell are $d$-block elements.

• In these elements $(n-1)d$ orbital is progressively filled.

• $d$-block elements are called transition elements because their properties are between $s$ and $p$ block elements and have incompletely filled $d$ sub shell in atomic and ionic state.

• The $(n-1)d$ subshell of $Zn$, $Cd$, $Hg$ and $Cn$ is completely filled in atomic and ionic state hence they are not considered as transition elements.

• $d$-block contains four transition series i.e., $3d$, $4d$, $5d$ and $6d$ having ten elements each.