Variable Oxidation States in d-block - NEET Notes, Formula & Common Mistakes
Variable Oxidation Statesd and f Block ElementsNEET ChemistryNEET 2025Transition MetalsOxidation StatesGeneral Properties
Variable Oxidation States in d-block - NEET Notes, Formula & Common Mistakes
d and f Block Elements·2 min read·NEET 2026
What NEET Asks
NEET often features questions on identifying oxidation states of transition metals in compounds/ions.
Expect questions on reasons for variable oxidation states and trends across the period/group.
Understanding stability of different oxidation states (e.g., d⁰, d⁵, d¹⁰ configurations) is crucial for 3-4 marks.
Key Points
Definition: Transition elements exhibit variable oxidation states due to the participation of both (n-1)d and ns electrons in bonding.
Reason: The energies of (n-1)d and ns orbitals are very close, allowing both sets of electrons to be available for bond formation.
Common Oxidation States: The most common oxidation state for many transition metals is +2 (loss of two ns electrons).
Trends: Oxidation states generally increase to a maximum at the middle of the series (e.g., Mn exhibits +7) and then decrease.
Stability: High oxidation states are more stable with highly electronegative elements like oxygen and fluorine (e.g., Mn₂O₇, K₂Cr₂O₇).
Examples: Sc (+3 only), Ti (+2, +3, +4), V (+2, +3, +4, +5), Cr (+2, +3, +6), Mn (+2, +3, +4, +6, +7), Fe (+2, +3), Co (+2, +3), Ni (+2, +3), Cu (+1, +2), Zn (+2 only).
Must-Know Formula / Reaction
Calculating Oxidation State:
For a neutral compound, sum of oxidation states = 0.
For an ion, sum of oxidation states = charge on ion.
Example: In KMnO₄
K (+1) + Mn(x) + 4 × O(-2) = 0
1 + x - 8 = 0
x = +7
Common Mistakes
Students often forget that Sc and Zn exhibit only one common oxidation state (+3 and +2 respectively).
Don't confuse the stability of high oxidation states with the commonness of low oxidation states (e.g., +2 for Mn is common, but +7 is highest).
Incorrectly calculating oxidation states in complex ions by ignoring the charge on ligands (e.g., CN⁻, C₂O₄²⁻).
Rapid Revision
Variable oxidation states arise from small energy difference between ns and (n-1)d orbitals. Highest state generally found with O/F. Sc (+3) and Zn (+2) are exceptions to variability. Mn shows highest (+7) in the 3d series.
Frequently Asked Questions
Why do d-block elements show variable oxidation states?▾
d-block elements show variable oxidation states because the energies of their outermost ns and (n-1)d orbitals are very close. This allows electrons from both these subshells to participate in chemical bonding, leading to multiple stable oxidation states.
Which d-block element shows the maximum number of oxidation states?▾
Manganese (Mn) from the 3d series shows the maximum number of oxidation states, ranging from +2 to +7. This is due to its electronic configuration, where all seven electrons (two 4s and five 3d) can be involved in bonding.
In what compounds are the highest oxidation states of transition metals usually observed?▾
The highest oxidation states of transition metals are typically observed in compounds with highly electronegative elements like oxygen and fluorine. These elements can stabilize higher oxidation states through strong covalent bonding and lattice energy effects, forming compounds like oxides and fluorides.
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