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161. The chemistry of the actinoid elements is not so smooth as that of the lanthanoids. Justify this statement by giving some examples from the oxidation state of these elements.

Among the actinoids, there is a greater range of oxidation states as compared to lanthanoids. This is in part due to the fact that 5f, 6d and 7s levels are of very much comparable energies and the frequent electronic transition among these three levels is possible. This 6d-5f transition and larger number of oxidation states among actinoids make their chemistry more complicated particularly among the 3rd to 7th elements. Following examples of oxidation states of actinoids. Justify the complex nature of their chemistry.

(i) Uranium exhibits oxidation states of+3, +4, +5, +6 in its compounds. However, the dominant oxidation state in actinoides is +3.

(ii) Nobelium, No is stable in +2 state because of completely filled f¹⁴ orbitals in this state.

(iii) Berkelium, BK in +4 oxidation state is more stable due to f⁷ (exactly half filled) configuration.

(iv) Higher oxidation states are exhibited in oxo ions are UO₂²⁺, PuO₂²⁺, NpO⁺ etc.

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Short Answer Type

162. Which is the last element in the series of the actinoids? Write the electronic configuration of this element. Comment on the possible oxidation state of this element.

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163.

Use Hund's rule to derive the electronic configuration of Ce³⁺ ion, and calculate its magnetic moment on the basis of 'spin only' formula.

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Long Answer Type

164. Name the members of the lanthanoid series which exhibit +4 oxidation states and those which exhibit + 2 oxidation states. Try to correlate this type of behaviour with the electronic configurations of these elements.

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Short Answer Type

165. Compare the chemistry of the actinoids with that of lanthanoids with reference to:
(i) electronic configuration (ii) oxidation states and (iii) chemical reactivity (iv) Atomic size

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166.

Explain:
CrO₄^2– is a strong oxidizing agent while MnO₄^2– is not.

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167.

Explain:
Zr and H_f have identical sizes.

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168.

Explain:
The lowest oxidation state of manganese is basic while the highest is acidic.

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169.

Explain:
Mn(II) shows maximum paramagnetic character amongst the divalent ions of the first transition series.

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Long Answer Type

170. Compare the general characteristics of the first series of the transition metals with those of the second and third series metals in the respective vertical columns. Give special emphasis on the following points:
(i) electronic configuration (ii) oxidation states (iii) ionisation enthalpies and (iv) atomic sizes.

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