(i) Write the electronic configuration of Cu²⁺, Z = 29 for Cu.

(ii) Discuss the oxidation states of lanthanides.

(iii) What is the trend in the ionic radii of transition elements?

(iv) Account for the fact that the second ionisation energies of both chromium and copper are higher than those of the next element.

(v) Why is manganese more stable in the +2 state than the +3 state while the reverse is true for iron?

(i) Cu atom contains 29 electrons but Cu²⁺ ion contains 27 electrons. These electrons are arranged as Cu²⁺ = 1s²2s²2p⁶3s²3p⁶3d⁹.



(ii) Typical oxidation state of all lanthanides is +3. Some lanthanides also exhibit +2 and +4 oxidation states in addition to +3. For example cerium forms salt in +4 oxidation state. Europium (II) salts are also known. These additional oxidation states are possible only because of the extra-stability of an empty half-filled or completely filled orbitals in some lanthanides. For example, in Ce⁴⁺ f-orbital is empty in Eu²⁺ and Yb²⁺ f-orbital is completely filled (4f¹⁴ 5d⁰6s⁰).


(iii) The ionic radii decrease with the increase in the atomic numbers of transition elements in a horizontal row. The decreasing trend is attributed to the increasing pull on the d-electrons by the nucleus.


(iv) In chromium and copper the second electron is lost from (n – 1) d-orbitals, whereas in the next higher element it is from ns.


(v) Mn²⁺ and Fe³⁺ have half-filled 3 d-orbitals that makes them more stable than Mn³⁺and Fe²⁺ respectively.