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Chemistry · 2022 · 3 marks
The d-and f-Block ElementsGeneral Properties of the Transition Elements (d-Block)3 marksUnderstandshort answer
CBSE 2022 · Region 1 · Set 1 · Q8
(a) Account for the following: (i) Transition elements have higher enthalpies of atomisation. (ii) Separation of a mixture of Lanthanoid elements is…
(a)
Account for the following :
(i)
Transition elements have higher enthalpies of atomisation.
(ii)
Separation of a mixture of Lanthanoid elements is difficult.
(iii)
The $\displaystyle \mathrm{E}^{\mathrm{o}}{ }_{\mathrm{M}^{2+} / \mathrm{M}}$ value for copper is positive.
OR
(b)
Define transition elements. Which of the d-block elements may not be regarded as the transition elements ? Why transition metals generally form coloured compounds ?
Marking-scheme solution
(a) (i) Because of greater number of unpaired electrons which cause strong metallic bonding / strong interatomic interaction forces.
(ii) Because of lanthanoid contraction / similar atomic or ionic radii / similar properties.
(iii) Because of high \(\displaystyle \Delta a H^{\circ}\) and low \(\displaystyle \Delta_{\text {hyd }} H^{\circ}\)
(b) The elements with partially filled or incompletely filled d-subshell either in the ground state or in the oxidation state.
Zinc, cadmium and mercury are not considered as transition elements.
Due to d-d transition or presence of unpaired d electrons.
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CBSE Class 12 Chemistry past-paper question from the 2022 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.