2.4.2Unit 2. Energetics, Group Chemistry, Halogenoalkanes and Alcohols
Reactivity – Groups 1 and 2 — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions
5 min read 4 parts Lesson 27 of 53 Unit quiz
Section 1 of 4Why Reactivity Increases
Reactivity of a metal is its tendency to lose electrons, so it follows the ease of ionisation.
1
Going down a group, each element has an extra electron shell, so the outer electrons are further from the nucleus.
2
The outer electrons are also shielded by more inner shells, so the attraction to the nucleus is weaker.
3
Less energy is needed to remove the outer electron or electrons, so metal atoms are oxidised more easily.
4
Group 1 and Group 2 reactions therefore become faster and more vigorous down the group.
5
Group 1 metals are more reactive than Group 2 metals in the same period because they lose only one electron.
Section 2 of 4Group 1 Reactions
With oxygen
- With oxygen Metals tarnish in air as a dull oxide forms, for example 4Li(s) + O₂(g) → 2Li₂O(s), and tarnishing is faster further down.
With chlorine
- With chlorine They burn to give white chlorides: 2Na(s) + Cl₂(g) → 2NaCl(s), with sodium burning with an orange flame.
With water
- With water 2M(s) + 2H₂O(l) → 2MOH(aq) + H₂(g) gives an alkaline solution and hydrogen gas.
Lithium
- Lithium Lithium fizzes steadily and moves on the surface, but does not melt.
Sodium and potassium
- Sodium and potassium Sodium melts into a ball and fizzes rapidly, while potassium ignites with a lilac flame.
Section 3 of 4Group 2 Reactions
Group 2 Reactions
With oxygen
- With oxygen 2Mg(s) + O₂(g) → 2MgO(s) burns with a bright white flame, and the other metals form oxides similarly.
With chlorine
- With chlorine Mg(s) + Cl₂(g) → MgCl₂(s) forms a white solid chloride.
With cold water
- With cold water Magnesium reacts very slowly, Mg(s) + 2H₂O(l) → Mg(OH)₂(s) + H₂(g), while calcium reacts steadily to give a cloudy solution.
With steam
- With steam Magnesium reacts vigorously with steam, Mg(s) + H₂O(g) → MgO(s) + H₂(g), giving a white oxide instead of the hydroxide.
Section 4 of 4Exam Checklist & Tips
2.4.2 – Key Points for the Exam
- Reactivity The tendency of a metal to lose electrons and form positive ions.
- Tarnishing The dulling of a metal surface as it reacts with oxygen to form an oxide layer.
- Alkaline solution A solution containing excess hydroxide ions, with pH above 7.
- Oxidised Describes an atom that has lost electrons, such as a metal forming M⁺ or M²⁺.
Common Mistakes
- Saying the metals become more reactive because the nuclear charge decreases; it increases but is outweighed.
- Forgetting that Group 1 reactions with water give hydrogen as well as the hydroxide.
- Writing Mg(OH)₂ as the product with steam instead of magnesium oxide.
- Omitting state symbols or using the wrong ratio of metal to water for Group 1 elements.
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