Supplement · Topic 9.4
The Electron Backpack Theory
Why do some metals react instantly while others barely flinch? It's all about how tightly they grip their electrons.
🎒
The Analogy: The Electron Backpack
Every metal atom carries outer electrons like a backpack. To become a positive ion (M⁺), it must throw that backpack away. The question is: how badly does it want to get rid of it?
⚡ Potassium
Backpack is on the 4th floor — throws it off a cliff before you say "go".
🔒 Copper
Superglues the backpack to its chest. Needs tremendous force to remove it.
Select a metal → click IONISE to remove the outer electron.
Electron Configuration
2881 ← outer
Ionisation Energy
419 kJ/mol
Energy needed to remove first outer electron
"Throws backpack off a cliff before you even say 'go'."
📖 One lonely electron on the 4th shell — miles from the nucleus. It FLIES off instantly!
🧩 Definition Builder
Click each piece to build the complete definition of reactivity:
📊 Reactivity Summary
| Metal | Ionisation Energy | Tendency to Form M⁺ | Ease of Oxidation |
|---|---|---|---|
| K — Potassium | 419 kJ/mol | 98% | Very easy |
| Na — Sodium | 496 kJ/mol | 82% | Very easy |
| Mg — Magnesium | 738 kJ/mol | 55% | Moderate |
| Fe — Iron | 762 kJ/mol | 30% | Slow |
| Cu — Copper | 745 kJ/mol | 5% | Very difficult |
9.4.11 · Tendency to Form Positive Ions · Cambridge IGCSE Chemistry 0620 (2026–2028) · Supplement
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