Variable Oxidation States
Simple Explanation
Unlike most main-group metals, transition elements commonly form compounds in several different oxidation states, because both their 4s electrons AND some of their 3d electrons are close enough in energy to be lost or involved in bonding.
Why Do We Need It?
This variability underlies an enormous range of transition-metal chemistry — the same element can form differently-coloured, differently-reactive compounds depending on its oxidation state, which is exploited constantly in catalysis, dyes, and analytical chemistry.
Worked Example
Determine the oxidation state of manganese in KMnO₄
Find the oxidation state of manganese in potassium permanganate, KMnO₄.
Why Does This Work?
Because 3d electrons are only slightly higher in energy than 4s electrons, once the 4s electrons are removed, additional 3d electrons can also be removed with a further, still manageable amount of energy — this is why iron can lose 2 electrons (Fe²⁺) or 3 (Fe³⁺), and manganese can be found in oxidation states from +2 all the way to +7.
Real-Life Example
Manganese's many oxidation states in everyday chemistry
Manganese compounds range from pale pink Mn²⁺ to deep purple MnO₄⁻ (permanganate, oxidation state +7).
Potassium permanganate (KMnO₄) is a common laboratory oxidising agent specifically because manganese in the +7 state is eager to be reduced to more stable, lower oxidation states like +2 — this reactivity comes directly from manganese's ability to access a wide range of oxidation states.
Practice
Find the oxidation state of chromium in K₂Cr₂O₇ (potassium dichromate). (K = +1, O = −2)
MediumCommon mistake
Assuming oxygen is ALWAYS −2 in every compound without exception — this is a reliable rule for the vast majority of compounds, but it breaks down in special cases like peroxides (where oxygen is −1); always double-check the compound type before applying the rule automatically.
Quick Review
- Transition elements commonly show multiple oxidation states.
- Both 4s and some 3d electrons are accessible for bonding/loss.
- Oxidation states can be calculated by balancing a compound's total charge to zero (or its ion charge).