Summary notes for AQA A-Level Chemistry Unit 3.2.2 - Group 2, the alkaline earth metals by an Imperial College London MSci Chemistry graduate. Notes divided into the following sections: Trends Down Group 2, Reactions of Groups 2 Metals with Water, Relative Solubilities of Group 2 Hydroxides in Wat...
Group 2, the Alkaline Earth Metals
Trends Down Group 2
Atomic Radius
Atomic radius increases down the group because…
•No. of shells ↑ down the group
•∴ more shielding + ∴ outer electrons further away from nucleus so…
•weaker nuclear attraction
First Ionisation Energy
First ionisation energy decreases down the group because…
•No. of shells ↑ down the group
•∴ more shielding + ∴ outer electron further away from nucleus so…
•weaker nuclear attraction ∴ outer electron held less tightly
•∴ easier to remove outer electron (requires less energy).
Melting Point
M.p.s decrease down the group because…
•Ions all have a +2 charge + same no. of delocalised electrons per atom.
•However, size of metal ions ↑ down the group ∴ atomic radius ↑
•∴ outer electrons further from nucleus so weaker nuclear attraction
•∴ strength of metallic bonding ↓
Reactions of Groups 2 Metals with Water
Magnesium
Reacts very slowly w/ warm water - few bubbles.
• Mg(s) + 2H2O(l) → Mg(OH)2 + H2
reactivity increases down the group
BUT, reacts vigorously w/ steam.
• Mg(s) + H2O(g) → MgO + H2
- MgO is formed rather than steam as the hydroxide is not stable at higher
temperatures + thermally decomposes to give MgO + H2O.
Calcium
Reacts w/ cold water + zzing is seen in an exothermic reaction. White ppt. forms.
• Ca + 2H2O → Ca(OH)2 + H2
Strontium
Reacts vigorously w/ cold water + zzing is seen in a highly exothermic reaction.
• Sr + 2H2O → Sr(OH)2 + H2
Barium
Reacts violently w/ cold water + zzing is seen in a highly exothermic reaction.
• Ba + 2H2O → Ba(OH)2 + H2
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