Ionization potential (ionization energy)
How much energy does it take to pull an electron off?
1. Electronic configurations and oxidation states
2. Why is sodium only +1?
Sodium has 11 electrons. Yet in all its compounds it is +1. You never meet Na²⁺.
Pick the right answer
Predict: why does sodium stop at +1?
- A. Removing a second electron costs far more energy
- B. Sodium has only one electron to give
- C. The second electron is farther from the nucleus
الشرح
Sodium's 1st electron comes from 3s, but the 2nd must leave the stable [Ne] arrangement in level n = 2, nearer the nucleus, so it costs far more energy (4562 vs 496 kJ/mol). That big jump is why sodium stops at +1.
3. Ionization potential
Ionization potential (ionization energy)
The energy needed to remove the most loosely held electron from a gaseous atom. Also called ionization energy.
Na(g) → Na+(g) + e-
The unit is kJ/mol. The farther the electron is from the nucleus, the weaker the pull, so less energy is needed.
4. Strip a sodium atom
Remove sodium's electrons one after another. Watch what each one costs.
electron removed 1
energy for electron 1 496 kJ/mol
1st electron: from 3s (n = 3). Na → Na+, now [Ne]
Successive ionization energies
The energies needed to remove the 1st, 2nd, 3rd … electrons of an atom, one after another.
5. The big jump
| Electron removed | Sodium (kJ/mol) |
|---|---|
| 1st | 496 |
| 2nd | 4562 |
| 3rd | 6910 |
Each one is larger: the electron leaves an ion that is more and more positive.
The 2nd costs about 9 times the 1st. It must leave the stable [Ne] arrangement, in level n = 2, nearer the nucleus.
So sodium gives up one electron only. The big jump tells you a representative metal's oxidation state.
6. Read the data
Pick the right answer
Metal X has these successive ionization energies: 578, 1817, 2745, 11577 kJ/mol. Which oxidation state does X show in its compounds?
- A. +3
- B. +1
- C. +4
- D. +2
الشرح
578 → 1817 → 2745 rise steadily; 11577 is the big jump. So X shows +3.
True or false?
The 2nd ionization energy is larger than the 1st because the 2nd electron is farther from the nucleus.
الشرح
The next electron is never farther. It is removed from a positive ion, so more energy is needed.
7. Summary
- Ionization potential (ionization energy): the energy to remove the most loosely held electron from a gaseous atom, in kJ/mol.
- Successive ionization energies increase, because each electron leaves a more positive ion.
- A big jump appears when the electron must leave a stable inner level: Na stops at +1.
| Metal | Big jump after | Oxidation state |
|---|---|---|
| Na | 1st electron | +1 |
| X (aluminum) | 3rd electron | +3 |
Next in Chapter 1: vanadium's energies rise gradually, with no big jump after its 4s electrons.
Can you explain why sodium forms Na+ but never Na²⁺?