  in chemistry, the term transition metal (or transition element) has two possible meanings: *the iupac definition defines a transition metal as "an element whose atom has a partially filled d sub-shell, or which can give rise to cations with an incomplete d sub-shell". *most scientists describe a "transition metal" as any element in the d-block of the periodic table, which includes groups 3 to 12 on the periodic table.r.h. petrucci, w.s. harwood and f.g. herring âgeneral chemistryâ (8th ed, prentice-hall 2002), p.341-2c.e. housecroft and a.g. sharpe âinorganic chemistryâ (2nd ed, pearson prentice-hall 2005), p.20-21 in actual practice, the f-block lanthanide and actinide series are also considered transition metals and are called "inner transition metals". jensen reviews the history of the terms "transition element" (or "metal") and "d-block". the word transition was first used to describe the elements now known as the d-block by the english chemist charles bury in 1921, who referred to a transition series of elements during the change of an inner layer of electrons (for example n=3 in the 4th row of the periodic table) from a stable group of 8 to one of 18, or from 18 to 32. ==classification== in the d-block the atoms of the elements have between 1 and 10 d electrons. {| class=wikitable border="1" cellpadding="4" cellspacing="0" style="margin:0.5em 1em 0.5em 0; text-align:center; background:; border: 1px solid ; padding:2px; font-size: 95%;" |- ! colspan=11 style="background-color:" | transition metals in the d-block |- style="background:" | ! group ! 3 !4 !5 !6 !7 !8 !9 !10 !11 !12 |- ! style="background:" | period 4 |sc 21 |ti 22 |v 23 |cr 24 |mn 25 |fe 26 |co 27 |ni 28 |cu 29 |zn 30 |- ! style="
Periodic_table Transition_metals