Edexcel A level Chemistry ms 2021/2022

Ionisation energy trend in Group 2 As you go down the group first ionisation energy decreases because: - Although nuclear charge is increasing - The electrons have an extra quantum shell of shielding making them easier to remove - They exist in a higher energy orbital (and/ or a further distance from the nucleus) Reactivity trend in group 2 Group 2 elements become more reactive going down a group as the outer two electrons are easier to remove because they have lower first ionisation energies. 00:02 01:38 Group 2 reactions with oxygen 2M(s) + O₂(g) - 2MO(s) This reaction occurs vigorously when heated, but even when not heated occurs very slowly Group 2 reactions with chlorine M(s) + Cl₂(g) - MCl(s) The group 2 element is heated with chlorine gas Group 2 reactions with water M(s) + 2H₂O(l) - M(OH)₂(aq) + H2(g) Magnesium reacts very slowly with water, calcium, strontium and barium do so with increasing vigor. Trends of solubility of group 2 hydroxides Solubility increases down the group as calcium hydroxide is only slightly soluble, so watch out for the state symbol change between calcium and strontium. PH value of these alkaline solutions depends not only on concentration but also on the solubility of the hydroxide. Reactions of group 2 oxides MO(s) + H₂O(l) - M(OH)₂(aq) A group 2 oxide reacts with water to form an alkali They also react with dilute acids in neutralisation reactions (as do hydroxides) Testing for carbon dioxide When carbon dioxide is passed through limewater (saturated aqueous solution of calcium hydroxide) it reacts with the calcium hydroxide to form calcium carbonate, a white precipitate that makes the solution go cloudy. CO2 + Ca(OH)2 - CaCO3 + H2O Milk of Magnesia Milk of Magnesia is a suspension of magnesium hydroxide in water and is used as an antacid as the OH ions neutralise the HCl in the stomach. OH ions can damage stomach lining, but Magnesium hydroxides low solubility means that there are few hydroxide ions in the solution. Trends of solubility of group 2 sulphates All group 2 nitrates and chlorides are soluble, but the solubility of sulphates decreases down the group. Calcium sulphate is slightly soluble, strontium and barium sulphate are completely insoluble. Barium Meals Barium sulphate is given to patients so that softer tissues show up on an x-ray. Barium ions are harmful to humans, but as barium sulphate is insoluble, the ions are not free to move Test for sulphate ions Add barium chloride (as the barium sulphate subsequently formed is insoluble and thus a white precipitate). Also add a dilute acid (such as nitric acid) to prevent other compounds such as barium carbonate being formed as a white precipitate.