What are the characteristics of the transition elements and why are they called transition elements? Which of the d-block elements may not be regarded as the transition elements?

What are the characteristics of the transition elements and why are th

1.	What are the characteristics of the transition elements and why are they called transition elements? Which of the d-block elements may not be regarded as the transition elements?
Answer» Solution :The general characteristics of transition elements are: (i) Electronic configuration: `(n-1) d^(1-10) ns^(1-2)` (II) Metallic character, Except Zn, Cd and Hg they show typical metallic properties. (III) Atomic size and ionic size: Ions of same charge in a given series show progressive decrease in radius with increasing atomic number (iv) Oxidation states: Except scandium, all elements show variable oxidation STAE in first series ranging from (+2) to (+7). (v) Paramagnetism: Ions with unpaired electrons are paramagnetic. (vi) Ionization enthalpy: Increases with effective nuclear charge. (vii) Formation of coloured ions: Presence of incompletely filled d-orbitals are responsible for the colour of ions. (viii) Formation of complex compounds: Due to HIGH nuclear charge and small size, metal ions FORM a complex compound. (ix) Catalytic properties: The ability to adopt multiple oxidation states make them good catalyst. (x) Formation of interstitial compounds. (xi) Alloy formation. They are called transition elements because of incompletely filled d-orbitals in ground state and in oxidized state. Zn, Cd, Hg have completely filld d-orbitlas `(d^(10))` in ground state as well as in its oxidized state. Hence, they are not considered transition elements.