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Transition and Inner Transition Elements — Chemistry STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 ScienceChemistryTransition and Inner Transition Elements4 Marks
Question
Write the electronic configuration of chromium and copper.
✓

Answer

Chromium $(_{24}Cr)$ has electronic configuration,
$_{24}Cr$ (Expected) : $Is^2 2s^2 2p^6 3s^2 3p^6 3d^4 4s^2$
(Observed) : $Is^2 2s^2 2p^6 3s^2 3p^6 3d^5 4s^1$Explanation :
  • The energy difference between $3d$- and $45$-orbitals is very low.
  • d-orbitals being degenerate, they acquire more stability when they are half-filled $(3d^5)$.
  • Therefore, there arises a transfer of one electron from $45$-orbital to $3d$-orbital in $Cr$ giving more stable half-filled orbital. Hence, the configuration of $Cr$ is $[Ar] 3d^5​​​​​​​$​​​​​​​ $4s^1$​​​​​​​ and not $[Ar] 3d^4​​​​​​​$​​​​​​​ $4s^2​​​​​​​$​​​​​​​.
Copper $(_{29}CU)$ has electronic configuration,
$_{29}Cu$ (Expected) : $Is^2 2s^3 2p^6 3s^3 3p^6 3d^9 4s^2$​​​​​​​
(Observed) : $Is^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^1$
Explanation :
  • The energy difference between $3d$- and $45$-orbitals is very low.
  • d-orbitals being degenerate, they acquire more stability when they are completely filled.
  • Therefore, there arises a transfer of one electron from $45$-orbital to $3d$-orbital in Cu giving completely filled more stable d-orbital.
Hence, the configuration of $Cu$ is $[Ar] 3d^{10}$​​​​​​​ $4s^1$​​​​​​​ and not $[Ar] 3d^9$ $4s^2​​​​​​​$​​​​​​​.

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