Why several oxidation states
Vanadium's gradual climb
1. Electronic configurations and oxidation states
2. Jump or ramp?
Sodium's 2nd ionization potential (also called ionization energy) is about 9 times its 1st. Vanadium loses its two 4s electrons first, then its 3d electrons.
Pick the right answer
Predict: when vanadium moves on from 4s to 3d electrons, what happens to the energy needed?
- A. A huge jump, like sodium's
- B. A gradual rise, with no huge jump
- C. It drops: 3d electrons are easier to remove
Explanation
Vanadium's 4s and 3d electrons are in sublevels close in energy, so its successive ionization potentials increase gradually, with no huge jump like sodium's.
3. One state or several?
Book point 5: the main transition elements have several oxidation states. Representative metals have one.
| Metal | Oxidation states |
|---|---|
| Na (group IA) | +1 |
| Mg (group IIA) | +2 |
| Al (group IIIA) | +3 |
| V (group VB) | +2, +3, +4, +5 |
| Mn (group VIIB) | +2, +3, +4, +6, +7 |
Why the difference? The answer is in the successive ionization potentials.
4. Strip vanadium, read the cost
Remove vanadium's electrons one at a time. Each step shows the book's ionization potential.
electrons removed 0
↑↓
4s↑↑↑
3dThe book's chart for vanadium
- V: 4s² 3d³ → V⁺: 4s¹ 3d³ (648)
- V⁺: 4s¹ 3d³ → V²⁺: 4s⁰ 3d³ (1346)
- V²⁺: 4s⁰ 3d³ → V³⁺: 4s⁰ 3d² (2858)
- V³⁺: 4s⁰ 3d² → V⁴⁺: 4s⁰ 3d¹ (4643)
- V⁴⁺: 4s⁰ 3d¹ → V⁵⁺: 4s⁰ 3d⁰ (6523)
5. A gradual rise
| Electron removed | Sodium (kJ/mol) | Vanadium (book) (kJ/mol) |
|---|---|---|
| 1st | 496 | 648 |
| 2nd | 4562 | 1346 |
| 3rd | 6910 | 2858 |
| 4th | 4643 | |
| 5th | 6523 |
Vanadium loses electrons from 4s and 3d in sequence. These two sublevels are close in energy.
So its ionization potentials increase gradually. No huge jump stops it, so several oxidation states can form.
6. Which metal is it?
Pick the right answer
Metal X: 738, 1451, 7733 kJ/mol. Metal Y: 659, 1310, 2653, 4175 kJ/mol. Which is a transition metal with several oxidation states?
- A. Y
- B. X
- C. Both: each list rises
- D. Neither: the values are too large
Explanation
X (magnesium): a big jump after the 2nd electron, so only +2. Y (titanium): a gradual rise, so several states.
True or false?
Transition metals have several oxidation states simply because they have many electrons.
Explanation
Calcium has 20 electrons, yet it has one oxidation state (+2), so the number of electrons is not the reason. Book point 5: the 4s and 3d electrons are close in energy, so the ionization potentials increase gradually.
7. Build the exam answer
Put in order
Give reasons: the main transition elements have several oxidation states. Put the answer in order.
- The atom is oxidized by losing electrons from the 4s and 3d sublevels
- These electrons are lost in sequence, and they are close in energy
- So the ionization potentials increase gradually (vanadium: 648, 1346, 2858 … kJ/mol)
- So several oxidation states can form
8. Summary
- Main transition elements have several oxidation states; representative metals (Na, Mg, Al) have one.
- They lose 4s and 3d electrons in sequence, and these are close in energy.
- So the ionization potentials increase gradually: vanadium 648, 1346, 2858, 4643, 6523 kJ/mol.
- Electrons lost from 4s and 3d in sequence → 4s and 3d are close in energy
- 4s and 3d are close in energy → Ionization potentials increase gradually (so)
- Ionization potentials increase gradually → Several oxidation states (so)
Back to the hook: can you explain why vanadium shows no huge jump between its 4s and 3d electrons?