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The d & f block elements-CBSE Class 12th NCERT Solution

Sep 4, 2013 17:41 IST

    Get, detailed solutions to the questions of the chapter The d & f block elements from NCERT textbooks. The objective is to helping students regarding the pattern of answering the question as per the cbse latest marking scheme.Cbse.jagranjosh.com provided you NCERT solutions for classes 12th math and science subjects.

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    Some questions of this chapter are given here.


    Q. Explain briefly how +2 state becomes more and more stable in the first half of the first row transition elements with increasing atomic number?

    Q. To what extent do the electronic configurations decide the stability of oxidation states in the first series of the transition elements? Illustrate your answer with examples.

    Answer. Transition elements show many oxidation states like Mn exhibiting maximum number of oxidation states (+2 to +7). The stability of +2 oxidation state increases with the increase in atomic number because more electrons are getting filled in the d-orbital.

    If we observe Scandium, it does not show +2 oxidation state as its electronic configuration is 4s2 3d1.Thus, by losing all three electrons, it attains stable noble gas configuration and becomes more stable. Similarly, Ti (+ 4) and V (+5) are very stable. In case of Mn, +2 oxidation state is very stable.

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    Q. Explain giving reasons:

    i. Transition metals and many of their compounds show paramagnetic behaviour.
    ii. The enthalpies of atomisation of the transition metals are high.
    iii. The transition metals generally form coloured compounds.
    iv. Transition metals and their many compounds act as good catalyst.

    Answer. i. Paramagnetic behaviour arises because of unpaired electrons. Transitionelements contain unpaired valence electrons in its d-orbital. Thus, they exhibit paramagnetic behaviour.
    ii. Because of high effective nuclear charge and a large number of valence electrons, transition elements form very strong metallic bonds. As a result, the enthalpy of atomization of transition metals is high.
    iii. In transition elements, absorption of radiation to promote an electron from one of the d−orbitals to another falls into visible region. In the presence of ligands, the d-orbitals split up into two sets of orbitals having different energies. Therefore, the transition of electrons can take place from one set to another. The energy required for these transitions is quite small and falls in the visible region of radiation. The ions of transition metals absorb the radiation of a particular wavelength and the rest is reflected, imparting colour to the solution.
    iv. The catalytic activity of the transition elements can be explained on followingfacts: -Ability to show multiple oxidation states and form complexes, transition metals form unstable intermediate compounds. Thus, they provide a new path with lower activation energy, Ea, for the reaction. Transition metals also provide a suitable surface for the occurrence of reaction.

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