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The D-And-f-Block Elements

Question
CBSEENCH12007200
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(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?

Solution
(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.

Some More Questions From The d-And-f-Block Elements Chapter

Silver atom has a completely filled d orbitals (4d10) in its ground state. How can you say that it is a transition element?

In the series Sc (Z = 21) to Zn(Z = 30), the enthalpy of atomisation of zinc is the lowest i.e., 26, kJ mol. Why?

The E° (M2+/M) value for copper is positive (+ 0.34 V). What is possibility the reason for this? 

How would you account for the irregular variation of ionisation enthalpies (first and second) in the first series of the transition elements?

Why is the highest oxidation state of a metal exhibited in its oxide or fluoride only?

Which is a stronger reducing agent Cr2+ or Fe2+ and why?

Explain why Cu+ ion is not stable in aqueous solutions?

Actinoid contraction is greater from element to element than lanthanoid contraction. Why?

On what ground can you say that scandium (Z = 21) is a transition element but zinc (Z = 30) is not?

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