Considering H2O as a weak field ligand, the number of unpaired electrons in [Mn(H2O)6]2+ will be

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  1. 5
  2. 2
  3. 4
  4. 3

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Option 1 : 5
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UP LT Grade General Knowledge Subject Test 1
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CONCEPT:

Weak Field Ligands and Crystal Field Splitting

  • Ligands like H2O are considered weak field ligands as they cause a small crystal field splitting in the d-orbitals of the central metal ion.
  • In the presence of weak field ligands, the crystal field splitting energy (Δo) is less than the pairing energy. Therefore, electrons prefer to remain unpaired and occupy higher energy orbitals, following Hund's rule.

EXPLANATION:

  • The given complex is [Mn(H2O)6]2+, where Mn is in the +2 oxidation state.
  • To determine the number of unpaired electrons:
    • The electronic configuration of Mn (atomic number 25) in its neutral state is: [Ar] 3d5 4s2.
    • In the Mn2+ ion, two electrons are removed (from the 4s orbital), so the configuration becomes: [Ar] 3d5.
  • Since H2O is a weak field ligand, the crystal field splitting energy is small, and the 3d electrons remain unpaired in the five d-orbitals.
  • Thus, all five electrons in the 3d orbitals of Mn2+ are unpaired.

Therefore, the number of unpaired electrons in [Mn(H2O)6]2+ is 5.

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