There are mainly four series of the transition metals,
3d series (Sc to Zn), 4d series (Y to Cd), 5d series (La
and Hf to Hg) and 6d series which has Ac and elements
from Rf to Cn The two series of the inner transition
metals; 4f (Ce to Lu) and 5f (Th to Lr) are known as
lanthanoids and actinoids respectively Originally the name transition metals was derived
from the fact that their chemical properties were
transitional between those of s and p-block elements Now according to IUPAC, transition metals are defined
as metals which have incomplete d subshell either in
neutral atom or in their ions