Transition metal

The thirty chemical elements 21 through 30, 39 through 48, and 71 through 80, are commonly referred to as the transition metals. This name comes from their position in the periodic table of elements, which represent the successive addition of electrons to the d orbitals of the atoms as one progresses through each of the three periods.

Main group elements prior to the appearance of the transition group elements in the periodic chart (ie, elements number 1 through 20) have no electrons in d atomic orbitals, but only in their s and p orbitals. (Though the low-lying, but empty d orbitals are thought to play a role in third-period elements such as silicon, phosphorus and sulfur)

                     /  Sc 21    Y 39   Lu 71   Lr 103    3 (IIIB)
                     |  Ti 22   Zr 40   Hf 72  Unq 104    4 (IVB)
                     |   V 23   Nb 41   Ta 73  Unp 105    5 (VB)
                     |  Cr 24   Mo 42    W 74  Unh 106    6 (VIB)
   transition metal /   Mn 25   Tc 43   Re 75  Uns 107    7 (VIIB)
                    \   Fe 26   Ru 44   Os 76  Uno 108    8 (VIIIB)
                     |  Co 27   Rh 45   Ir 77  Une 109    9 (VIIIB)
                     |  Ni 28   Pd 46   Pt 78            10 (VIIIB)
                     |  Cu 29   Ag 47   Au 79            11 (IB)
                      \ Zn 30   Cd 48   Hg 80            12 (IIB)

Transition metals tend to be coloured. Many of them are also good catalysts; iron is the catalyst for the Haber process.