The elements lying in the middle of periodic table belonging to groups 3 to 12 are known as d-block or the transition elements. They are all metals. Their general electronic configuration is (n – 1)d1–10 ns1–2 where (n – 1) stands for penultimate (last but one) shell and the d orbital may have 1 to 9 electrons and s orbital of the ultimate shell (last shell) 'n' may have 1 to 2 electrons. Zinc, cadmium, mercury do not correspond to this electronic configuration. Their electronic configuration is represented by a general formula (n - 1)d1–10 ns2. They differ from transition elements in their properties due to completely filled d-orbital. They are not regarded as transition metals. Pd has exceptional outer electronic configuration 5s04d10.
It is the heat required to convert 1 mole of crystal lattice into free atoms. Transition elements have high enthalpy of atomization.
The electric potential developed on a metal electrode when it is in equilibrium with a solution of its ions, leaving electrons from the electrode.
The oxides in which oxygen and metal are not in whole number, are called non-stoichiometric oxides. e.g., Fe0.91 or Fe0.95, etc.
They are special type of mixed oxides in which structure is characterized by the fact that the oxygen atoms constitute a face-centred cubic lattice, e.g., ZnFe2O4, is normal spinel in which trivalent ions occupy the octahedral holes and divalent ions occupy the tetrahedral holes.
There is steady decrease in the atomic and ionic radii as the atomic number increases. It is because, for every additional proton in the nucleus, the corresponding electron goes into the 4f shell which is too diffused to screen the nucleus as effectively as more localized inner shell. Hence, the attraction of the nucleus for the outermost electrons increases steadily with the atomic number of the lanthanoids. This contraction in size is quit regular. This is called lanthanoid contraction.
Transition metals have high enthalpy of atomization due to strong metallic bond which is due to smaller atomic size and additional covalent bond due to d-doverlapping.
Most of transition. metals are paramagnetic in nature due to presence of unpaired electrons. It increases from Sc to Cr and then decreases because number of unpaired electron increases from Se to Cr and then decreases. Among divalent cations Mn2+ has 5 unpaired electron, therefore most paramagnetic. Cu+(3d10) is diamagnetic due to no unpaired electrons but Cu2+ (3d9) is paramagnetic due to presence of unpaired electron. Fe3+ is more paramagnetic (5 unpaired electrons) then Fe2+ (4 unpaired electrons).
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