IGCSE Chemistry Group 1 (Alkali Metals) Notes
Group 1 metals — Li, Na, K, Rb, Cs — are soft, low-density metals with one outer electron. Reactivity increases down the group.
Key concepts
- One outer electron
- All Group 1 metals form 1+ ions by losing this electron.
- Trend in reactivity
- Down the group, atoms get bigger, outer electron is further from the nucleus and more shielded, so it is lost more easily.
- Reaction with water
- 2M + 2H₂O → 2MOH + H₂. Fizzing, floats, and hotter reactions further down the group.
- Lithium: fizzes gently.
- Sodium: melts into a shiny ball, fizzes quickly, may catch fire.
- Potassium: bursts into a lilac flame instantly.
- All products dissolve to give strongly alkaline solutions (turn universal indicator purple).
Worked example
Explain why potassium is more reactive than sodium.
- 1Potassium has one more electron shell than sodium.
- 2Its outer electron is further from the nucleus.
- 3It is also shielded by more inner electrons.
- 4So the attraction is weaker and the outer electron is lost more easily, making potassium more reactive.
Answer: Larger atom + more shielding → weaker attraction on outer electron → lost more easily.
Common mistakes
✗ Saying reactivity increases because atoms get 'bigger and more reactive'.
✓ Explain properly: bigger atom, more shielding, weaker attraction, easier to lose the outer electron.
✗ Balancing incorrectly, e.g. 2Na + H₂O → …
✓ Always: 2Na + 2H₂O → 2NaOH + H₂.
✗ Missing observations.
✓ Fizzes, floats, moves, may catch fire — mention all four where relevant.
Quick check
Try these, then reveal the answers.
What flame colour is seen with potassium in water?Reveal answer
Lilac.
What gas is produced when Group 1 metals react with water?Reveal answer
Hydrogen.
Why must Group 1 metals be stored in oil?Reveal answer
To keep them away from air and water, which they react with.
Exam tips
- Structure explanations: distance from nucleus, shielding, attraction, ease of losing electron.
- Always balance the water equation with 2 in front of both the metal and the water.
- Predict rubidium/caesium by extending the trend (more vigorous / explosive).
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Frequently asked questions
Why do all alkali metals form 1+ ions?+
Because they have exactly one electron in their outer shell, which they lose to reach a full outer shell.
Why do the solutions formed turn universal indicator purple?+
The metal hydroxide produced (e.g. NaOH) is a strong alkali with a high pH.
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