GROUP 2 – ALKALI METALS
TRENDS: REACTIONS WITH WATER:
ATOMIC RADIUS: TREND: [reactivity] increases down group
TREND: increases EXPLANATION: shielding increases down group
EXPLANATION shielding increases down group 2 Outer e- less attracted to p+ in nucleus
Effective nuclear charge weakens Outer electron easily lost
IONISATION ENERGY: REACTIONS
TREND: Decreases General equation: X(s) + 2H2O(l) X(OH)2(aq) + H2(g)
EXPLANATION: shielding increases Be: doesn’t react
Outer electron has a weaker attraction to p in nucleus Mg: VERY steadily
Less energy required to lose outer electron Ca: steadily
Sr: fairly quickly
REACTIVITY: Ba: rapidly
TREND: Increases
EXPLANATION: shielding increases down the group With steam, they would make metal oxides (e.g. MgO) and
Weaker nuclear attraction between outer e and nucleus Hydrogen
Less energy required to remove it
USES OF METAL HYDROXIDES:
MELTING POINT: Mg(OH)2: used in medicine to neutralise excess acid in
TREND: Decrease stomach
EXPLANATION: metallic bond strength decreases Treats constipation
As size of ion increases Used for indigestion tablets and heartburn
Attraction btw delocalised e- and p+ in nucleus weakens
Less energy required Ca(OH)2: used in agriculture to neutralise soil
Used to test for CO2 when dissolved in water
Ca(OH)2 +CO2 CaCO3 + H2O
TRENDS: REACTIONS WITH WATER:
ATOMIC RADIUS: TREND: [reactivity] increases down group
TREND: increases EXPLANATION: shielding increases down group
EXPLANATION shielding increases down group 2 Outer e- less attracted to p+ in nucleus
Effective nuclear charge weakens Outer electron easily lost
IONISATION ENERGY: REACTIONS
TREND: Decreases General equation: X(s) + 2H2O(l) X(OH)2(aq) + H2(g)
EXPLANATION: shielding increases Be: doesn’t react
Outer electron has a weaker attraction to p in nucleus Mg: VERY steadily
Less energy required to lose outer electron Ca: steadily
Sr: fairly quickly
REACTIVITY: Ba: rapidly
TREND: Increases
EXPLANATION: shielding increases down the group With steam, they would make metal oxides (e.g. MgO) and
Weaker nuclear attraction between outer e and nucleus Hydrogen
Less energy required to remove it
USES OF METAL HYDROXIDES:
MELTING POINT: Mg(OH)2: used in medicine to neutralise excess acid in
TREND: Decrease stomach
EXPLANATION: metallic bond strength decreases Treats constipation
As size of ion increases Used for indigestion tablets and heartburn
Attraction btw delocalised e- and p+ in nucleus weakens
Less energy required Ca(OH)2: used in agriculture to neutralise soil
Used to test for CO2 when dissolved in water
Ca(OH)2 +CO2 CaCO3 + H2O
