3.1.2 Group 2

Question 1

trend in atomic radius down group

Answer 1

increases
due to increased electrons, increased shielding
atom is bigger

Question 2

trend in melting points down the group

Answer 2

decrease
metallic bond weakens as atomic size increases
distance between positive ions and delocalised electrons increases
therefore the electrostatic attraction between the positive ions and delocalised electrons decreases
weaker bonds so less energy required to break them

Question 3

trend in first and second ionisation energies down the group

Answer 3

decrease
outermost are held more weakly as they are successively further away from the nucleus in additional shells
outer shell electrons are more shielded from the attraction of the nucleus by repulsive force of inner electrons

Question 4

trend in reactivity down the group

Answer 4

increases
atomic radius increases, increased shielding, nuclear attraction decreases and it is easier to remove outer shell electrons

Question 5

what are the reactions of group 2

Answer 5

with oxygen
with water
with acid
metal oxides with water

Question 6

reactions with oxygen

Answer 6

form metal oxides

2Mg + O2 -> 2MgO

Mg burns with bright white flame, MgO is a white solid with high MP and BP

Question 7

reactions with water

Answer 7

Mg react with steam to produce metal oxide and hydrogen
Mg react with warm water to produce metal hydroxide and hydrogen (much slower reaction)
Group 2 metals react with cold water to produce hydroxides and hydrogen

Question 8

what do hydroxides do to the water in the solution

Answer 8

make the water alkaline

Question 9

what would you observe in the reaction between metals and water

Answer 9

fizzing
metal will dissolve
solution will heat up
with calcium a white ppt (less ppt forms down the group)

Question 10

reactions with acid

Answer 10

forms a salt and hydrogen

Question 11

reactions with metal oxides and water

Answer 11

form hydroxides of varying solubility

Question 12

use of calcium hydroxide

Answer 12

reasonably soluble
used in agriculture to neutralise acidic soils
if too much is used then soil becomes too alkaline to sustain crop growth

Question 13

use of aqueous calcium hydroxide

Answer 13

called lime water and is used to test for the presence of carbon dioxide
limewater turns cloudy as white calcium carbonate is produced

Question 14

use of magnesium hydroxide

Answer 14

partially soluble in water
a suspension in water will have a slight alkaline pH
used in medicine as milk of magnesia to neutralise excess acid in the stomach and treat constipation (will form magnesium chloride and water)