Oxidation states from Sc to Zn
Up to manganese, then down
1. Electronic configurations and oxidation states
2. Twelve electrons, how many states?
Manganese has 7 electrons in 4s and 3d, and it reaches +7 in KMnO4. Zinc has 12 electrons in 4s and 3d.
Pick the right answer
Predict: what is zinc's highest oxidation state in the book's table?
- A. +12: it loses all its 4s and 3d electrons
- B. +2
- C. +7, like manganese
الشرح
Zinc's highest oxidation state in the table is +2. The highest state rises from Sc up to Mn (+7), then decreases gradually to +2 in zinc.
3. Walk the book's table
Slide from Sc to Zn. For each element, compare the two numbers.
atomic number Z 21
Sc (Z = 21), group IIIB
[Ar]\ 4s²\ 3d¹. Oxidation states: +3
electrons in 4s + 3d 3
highest oxidation state +3
Compounds: Sc2O3
Book table, p.8 (for illustration only). Copper's row is printed with a typo; its states are +1 and +2.
4. Up to Mn, then down
| Element | Electrons in 4s + 3d | Highest oxidation state |
|---|---|---|
| Sc | 3 | 3 |
| Ti | 4 | 4 |
| V | 5 | 5 |
| Cr | 6 | 6 |
| Mn | 7 | 7 |
| Fe | 8 | 6 |
| Co | 9 | 4 |
| Ni | 10 | 4 |
| Cu | 11 | 2 |
| Zn | 12 | 2 |
From Sc to Mn, the highest state uses all the 4s and 3d electrons.
After Mn, the highest state decreases gradually, to +2 in zinc.
5. Read a state from a formula
The table lists compounds. Find each metal's oxidation state with the sum-to-zero rule.
Worked: vanadium in V₂O₅
Call vanadium x. Two V atoms give 2x; five O atoms give 5 × (−2).
2x + 5(-2) = 0 \;\; 2x = +10 \;\; x = +5
+5 is vanadium's highest state: it has lost all 5 of its 4s and 3d electrons.
Your turn: iron in Na₂FeO₄
Fill in the blanks
In Na2FeO4 (Na = +1, O = −2), iron is _____ .
الشرح
2(+1) + x + 4(−2) = 0, so x = +6. Iron's highest state is +6, not +8.
Need a hint?
- Two Na atoms give +2.
- Four O atoms give −8.
- +2 + x − 8 must equal 0.
6. The group number limit
| Group | Elements | Highest state |
|---|---|---|
| IIIB to VIIB | Sc, Ti, V, Cr, Mn | +3, +4, +5, +6, +7 |
| VIII | Fe, Co, Ni | +6, +4, +4 |
| IB | Cu | +2 |
| IIB | Zn | +2 |
Book point 4: the maximum oxidation state does not exceed the group number. Group VIII stays well below 8.
7. Why no Sc⁴⁺?
Sc atom
↑↓
4s↑
3dSc³⁺
4s
3d
Scandium has only three electrons in 4s and 3d. Sc³⁺ has lost all three.
Sc³⁺ has the stable configuration of argon. A fourth electron would have to come from that stable arrangement.
8. Use the rules
Pick the right answer
Molybdenum (Mo) is below chromium, in group VIB. By the book's rule, its highest oxidation state cannot exceed:
- A. +6
- B. +7
- C. +2
- D. +4
الشرح
Group VIB → the maximum cannot exceed +6.
Fill in the blanks
In K2Cr2O7, chromium is _____ . This is _____ its group number (type: below / equal to / above).
الشرح
2(+1) + 2x + 7(−2) = 0, so x = +6. That equals its group number (VIB).
Need a hint?
- K counts +1 and O counts −2.
- Two K give +2; seven O give −14.
- Two Cr atoms share the rest.
9. Gold and titanium
Pick the right answer
In AuCl3, gold is +3. Gold is in group IB. What does this show?
- A. Group IB is the book's exception: its maximum can exceed the group number
- B. The value must be a mistake
- C. Gold is not in the first series, so the book's rule says nothing
- D. The maximum always equals the group number
الشرح
It shows the book's exception: the maximum oxidation state does not exceed the group number except in group IB (copper, silver and gold). Gold, in group IB, reaches +3.
True or false?
Titanium does not form Ti⁵⁺ for the same reason that scandium does not form Sc⁴⁺.
الشرح
Ti: [Ar]\ 4s²\ 3d². Ti⁴⁺ = [Ar], the same stable arrangement as Sc³⁺.
10. Summary
- The highest state rises from Sc (+3) to Mn (+7), then decreases to Zn (+2). Zinc has 12 electrons in 4s and 3d, yet only +2.
- From Sc to Mn it equals the number of 4s and 3d electrons. After Mn it is lower: Fe +6, Co and Ni +4.
- The maximum does not exceed the group number, except group IB (Cu shows +2).
- Sc³⁺ is [Ar], so there is no Sc⁴⁺.
Can you explain why vanadium's highest state is +5 and not +6?
Reveal
Vanadium is [Ar]\ 4s²\ 3d³: it has 5 electrons in 4s and 3d. At +5 it has lost all of them, and +5 is also its group number (VB). So its highest state is +5.