number of unpaired electrons increases from Sc to Cr and then decreases .
g . Catalytic properties : Most of transition metals are used as catalyst because of ( i ) presence of incomplete or empty d – orbitals , ( ii ) large surface area , ( iii ) varuable oxidation state , ( iv ) ability to form complexes , e . g ., Fe , Ni , V 2 O 3 , Pt , Mo , Co and used as catalyst .
h . Formation of coloured compounds : They form coloured ions due to presence of incompletely filled d – orbitals and unpaired electrons , they can undergo d – d transition by absorbing colour from visible region and radiating complementary colour .
i . Formation of complexes : Transition metals form complexes due to ( i ) presence of vacant d – orbitals of suitable energy ( ii ) smaller size ( iii ) higher charge on cations .
j . Interstitial compounds : Transition metals have voids or interstitials in which C , H , N , B etc . can fit into resulting in formation of interstitial compounds . They are non – stoichiometric , i . e ., their composition is not fixed , e . g ., steel . They are harder and less malleable and ductile .
k . Alloys formation : They form alloys due to similar ionic size . Metals can replace each other in crystal lattice , e . g ., brass , bronze , steel etc .