MHT-CET Chemistry · Transition and Inner Transition Elements

Oxidation States of Transition Elements

Transition elements show several oxidation states because their (n−1)d and ns electrons are close in energy and can be lost in steps; the range is widest in the middle of the 3d series, at manganese (+2 to +7), narrowest at the ends — scandium +3 (and +2), zinc only +2 — and the highest state in the whole block is +8, reached by osmium in the 5d series.

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Why this matters

11 PYQs, none HARD. Of the six set from 2021 to 2025, two ask which 3d element shows the most oxidation states (Mn), one which shows the fewest (Zn), one Scandium's states, one the highest state in the third series (+8), and one the Stock notation of MnO₂. One card.

Concept 1 of 1: How Many Oxidation States, and the Highest One

The highest oxidation state an early 3d element can reach is the number of its 4s plus 3d electrons: Sc +3, Ti +4, V +5, Cr +6, Mn +7. After manganese the d electrons start pairing and hold on more tightly, so the maximum falls again (Fe +6, Co +4, Ni +4, Cu +2, Zn +2). Manganese therefore has the widest range, +2 to +7. The ends are narrow: scandium mostly +3, zinc only +2. Going down a group higher states become MORE stable, so the 5d series reaches +8 in OsO₄. Stock notation just writes the state in Roman numerals: MnO₂ has Mn at +4, Mn(IV)O₂.

Definition

Most states in the 3d series: Mn, +2 to +7 (4s² 3d⁵ — all seven outer electrons can be used).
Fewest: Zn, only +2 (fewer than Sc, Ti or Cu).
Scandium: +2, +3 (+3 the stable one, giving Sc³⁺ d⁰).
Highest state in the d-block: +8, by Os in $\text{OsO}_4$ (5d); the maximum in the 3d series is +7 (Mn in $\text{MnO}_4^-$ ).
Stock notation: oxidation state in Roman numerals — $\text{MnO}_2$ : $x + 2(-2) = 0$ , so Mn(IV)O₂; $\text{KMnO}_4$ is Mn(VII).

Maximum oxidation state, Sc to Mn

\text{max O.S.} = n(4s) + n(3d):\ \text{Sc } {+3},\ \text{Ti } {+4},\ \text{V } {+5},\ \text{Cr } {+6},\ \text{Mn } {+7}

Worked example

Give the oxidation state of Cr in K₂Cr₂O₇ and write it in Stock notation.

Practise this conceptself-check · 4 quick reps

The same idea in a real exam question:

MHT-CET · 2023 · 11th May Shift 1 · Q76Easy

Example 1 · Transition and Inner Transition Elements · Oxidation States of Transition Elements

Which element from following exhibits highest number of various different possible oxidation states?

Picking the element with most d electrons

Zinc and copper have the most d electrons but the fewest states — a full or nearly full d subshell does not give up electrons. The widest range belongs to the middle, Mn.

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Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Formulas (1)

How Many Oxidation States, and the Highest One
Maximum oxidation state, Sc to Mn
$\text{max O.S.} = n(4s) + n(3d):\ \text{Sc } {+3},\ \text{Ti } {+4},\ \text{V } {+5},\ \text{Cr } {+6},\ \text{Mn } {+7}$

Watch out for (1)

Picking the element with most d electrons
→ How Many Oxidation States, and the Highest One

Test yourself on Transition and Inner Transition Elements

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