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Why is Cr^(2+) reducing and Mn^(3+) oxid...

Why is `Cr^(2+)` reducing and `Mn^(3+)` oxidising when both have `d^(4)` configuration ?

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`Cr^(2+)` is reducing as its configuration changes from `d^(4)` to `d^(3)`, the latter having a half-filled `t_(2g)` level (see Unit 9) . On the other hand, the change from `Mn^(3+)` to `Mn^(2+)` results in the half-filled `(d^(5))` configuration which has extra stability.
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(a) What happens when (i) Manganate ions (MnO_(4)^(2-)) undergoes diSQProportionation reaction in acidic medium ? (ii) Lanthanum is heated with Sulphur? (b) Explain the following trends in the properties of the members of the First series of transition elements: (i) E^(@) (M^(2+)//M) value for copper is positive (+ 0.34 V) in contrast to the other members of the series. (ii) Cr^(2+) is reducing while Mn^(3+) is oxidising, though both have d^(4) configuration. (iii) The oxidising power in the series increases in the order VO_(2)^(+) lt Cr_(2)O_(7)^(2-) lt MnO_94)^(-) .

Assertion : Cr^(2+) is reducing and Mn^(3+) is oxidising. Reason : Cr^(2+) and Mn^(3+) have d^4 configuration.

The ion Cr^(2+) is redusing agent while that of Mn^(3+) is an oxidising agent though both have 3d^(4) configuration. This is because

Assertion :- Cr^(+2) is a reducing agent and Mn^(+3) is oxidising agent. Reason :- Mn^(+3) has d^(5) configuration.

How would you account for the following: (i) Cr^(2+) is reducing in nature while with the same d-orbital configuration (d^(4)) Mn^(3+) is an oxidising agent (ii) In a transition series of metals, the metal which exhibits the greatest number of oxidation state occurs in the middle of the series.

How would you account for the following? (i) Cr^(2+) is reducing in nature while with the same d-orbital configuration (d^14) Mn^(3+) is an oxidising agent. (ii) In a transition series of metals, the metal which exhibits the greatest number of oxidation states occurs in the middle of the series. (iii) Metal-metal bonding is more frequent for the 4d and the 5d series of transition metals than for the 3d series.

NCERT-THE D AND F BLOCK ELEMENTS-Exercise
  1. Why is Cr^(2+) reducing and Mn^(3+) oxidising when both have d^(4) con...

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  2. Write down the electronic configuration of: (i). Cr^(3+) (ii). Pm^...

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  3. Why are Mn^(2+) compounds more stable than Fe^(2+) toward oxidation to...

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  4. Explain briefly how +2 state become more and more stable in the first ...

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  5. To what extent do the electronic configurations, decide the stability ...

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  6. What may be the stable oxidation state of the transition element with ...

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  7. Name the oxometal anions of the first series of the transition metals ...

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  8. What is lanthanoid contraction? What are the consequences of lanthanol...

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  9. What are the characteristics of the transition elements and why are th...

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  10. In what way is the electronic configuration of the transition elements...

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  11. What are the different oxidation states exhibited by the lanthanoids?

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  12. Explain gives reason. (a) Transition metal and many of their compoun...

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  13. What are interstitial compounds? Why are such compounds well known for...

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  14. How is the variability in oxidation states of transition metals differ...

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  15. Describe the preparation of potassium dichromate from iron chromite or...

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  16. Describe the oxidising action of potassium dichromate and write the io...

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  17. Describe the preparation of potassium permanganate. How does the acidi...

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  18. For M^(2+)//M and M^(3+)//M^(2+) systems the E^(ϴ) values for some met...

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  19. Predict which of the following will be coloured in aqueous solution? ...

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  20. Compare the stability of +2 oxidation state for the elements of the fi...

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  21. Compare the chemistry of actinoids with that of the lanthanoids with s...

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