How would you account for the following situations(i) The transition m

1.	How would you account for the following situations(i) The transition metals generally form coloured compounds.(ii) With 3d4 configuration, Cr2+ acts as a reducing agent but Mn3+ acts as an oxidising agent (Atomic masses, Cr = 24, Mn = 25)(iii) The actinoids exhibits a larger number of oxidation states than the corresponding lanthanoids.
Answer» (i) Colour of compounds of transition elements depends upon the unpaired electrons present in d orbitals of transition elements. If d orbitals are completely vacant as in Sc³⁺, Ti⁴⁺ or completely filled as in Cu²⁺, Zn²⁺, the compounds will be colourless. But if any unpaired electron is present in d-orbitals, the compound will be coloured due to d → d transition. The unpaired electron is excited from one energy level to another energy level within the same d subshell. For this purpose (d → d transition), the energy is absorbed from visible region of radiation and reflected light will decide the colour of the compound. (ii) Cr²⁺ is strongly reducing in nature. It has a d⁴ configuration. While acting as a reducing agent, it gets oxidised to Cr³⁺ (electronic configuration d³). This d³ configuration can be written as t₂³ configuration, which is a more stable configuration. In the case of Mn³⁺ (d⁴) it Mn²⁺ (d⁵). This has an exactly half filled d – orbital and is highly stable. (iii) Actinoids show a large number of oxidation states because of small energy gap between 5f, 6d and 7s subshells.

How would you account for the following situations(i) The transition metals generally form coloured compounds.(ii) With 3d4 configuration, Cr2+ acts as a reducing agent but Mn3+ acts as an oxidising agent (Atomic masses, Cr = 24, Mn = 25)(iii) The actinoids exhibits a larger number of oxidation states than the corresponding lanthanoids.

Answer»

(i) Colour of compounds of transition elements depends upon the unpaired electrons present in d orbitals of transition elements. If d orbitals are completely vacant as in Sc³⁺, Ti⁴⁺ or completely filled as in Cu²⁺, Zn²⁺, the compounds will be colourless. But if any unpaired electron is present in d-orbitals, the compound will be coloured due to d → d transition. The unpaired electron is excited from one energy level to another energy level within the same d subshell. For this purpose (d → d transition), the energy is absorbed from visible region of radiation and reflected light will decide the colour of the compound.

(ii) Cr²⁺ is strongly reducing in nature. It has a d⁴ configuration. While acting as a reducing agent, it gets oxidised to Cr³⁺ (electronic configuration d³). This d³ configuration can be written as t₂³ configuration, which is a more stable configuration. In the case of Mn³⁺ (d⁴) it Mn²⁺ (d⁵). This has an exactly half filled d – orbital and is highly stable.

(iii) Actinoids show a large number of oxidation states because of small energy gap between 5f, 6d and 7s subshells.

Discussion

No Comment Found

Related InterviewSolutions

Reply to Comment