d and f Block Elements — CBSE Class 12 · 2016 · Delhi Board Question with Solution

Give reasons:
i) Mn shows the highest oxidation state of +7 with oxygen, but with fluorine it shows a highest oxidation state of only +4.
ii) Transition metals show variable oxidation states.
iii) Actinoids show irregularities in their electronic configurations.

Solution

(i) Oxygen can form multiple bonds (pπ–dπ) with the metal, so just four O atoms carry Mn to +7 in Mn

_{2}

_{7}

(each O counts −2). Fluorine forms only single bonds; +7 would demand seven F atoms crowded round Mn, which bond energetics and sterics forbid — so the highest fluoride is MnF

_{4}

(+4).
(ii) The (n−1)d and ns orbitals are very close in energy; besides the ns electrons, a varying number of d electrons can also be used in bonding — hence states differing by single units.
(iii) In the actinoids the 5f and 6d subshells are almost equal in energy, so electrons occupy whichever combination happens to be more stable (extra stability of f

^{0}

, f

^{7}

, f

^{14}

also intervenes) — producing irregular configurations (e.g. Th: 6d

^{2}

^{2}

with no 5f electron).

CBSE Class 12 Board · 2016 · Delhi · Subjective

CBSE Class 12 · 2016 · Delhi · d and f Block ElementsShort Answer

Solution

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