Group 2

• group 2 elements have high melting points because they have giant metallic structure with strong metallic bonds (so strong electrostatic forces of attraction between positive ions and delocalised electrons) which require a lot of energy to break
• Group 2 elements are harder and have a higher density than group 1 elements because their ions have a higher charge so electrons are held more tightly so they are smaller and pack more closely together
• Group 2 elements are all reactive metals with similar chemical reactions because they all have 2 electrons in their outer shell
• Group 2 compounds are ionic compounds and generally white crystalline solids
• atomic radius increases down group 2 because there are more shells so more shielding so nucleus has a weaker attraction for the outer electrons so electrons are held less tightly
• first ionisation energy decreases down group 2 because there are more shells and more shielding so nuclear attraction for the electron being removed is weaker so it is easier to remove an electron
• melting point decreases down group 2 as metallic bonds get weaker as there are more shells and more shielding so attraction between positive ions and delocalised electrons gets weaker
• reactivity increases down group 2 as elements react by losing electrons and going down the group there are more shells so more shielding so attraction bwtween nucleus and electron being lost is weaker
• in the reaction of magnesium with cold water: very slow reaction with few bubbles seen. Magnesium is sparingly soluble. Mg(s) + 2H2O(l) -> Mg(OH)2(s) + 2H2(g)
• in the reaction of magnesium with steam: bright white light and white power/solid formed. Mg(s) + H2O(g) -> MgO(s) + H2(g)
• in the reaction of calcium with cold water: effervescence and white solid are formed (Ca(OH)2 is slightly soluble). Ca(a) + 2H2O(l) -> Ca(OH)2(aq) + 2H2
• in the reaction of strontium with cold water: effervescence and less white solid is seen (Sr(OH)2 is more soluble than Ca(OH)2). Sr(s) + 2H2O(l) -> Sr(OH)2(aq) + 2H2(s)
• in the reaction of barium with cold water: effervescence and a colourless solution can be seen (all Ba dissolves) Ba(s) + 2H2O -> Ba(OH)2 (aq) + 2H2(g)
• reactivity of group 2 elements with water increases down the group as electrons are more easily lost. M(s) + H2O(l) -> M(OH)2 + H2(g)
• in the reaction of group 2 elements with water, the oxidation state of the group 2 element goes from 0 to +2 and hydrogen goes from +1 to 0
• Titanium is strong and has a high melting point and high corrosion resistance. It is difficult to extract from its ores eg TiO2 because reduction with carbon produces brittle TiC (titanium carbide). To avoid this TiO2 ore is first reacted with Cl and C to form TiCl4.
• TiO2 + 2Cl2 + 2C -> TiCl4 + 2CO
• Titanium is then reduced with magnesium to produce titanium. TiCl4 + 2Mg -> Ti + 2MgCl2. Magnesium is the reducing agent.
• Titanium has application in the aerospace, marine and motor vehicle industries
• Group 2 hydroxides are bases and react with acids e.g M(OH)2 + 2HCl —> MCl2 + H2O
• Group 2 hydroxides increase in solubility and pH going down the group, so magnesium hydroxide is sparingly soluble and barium hydroxide is soluble
• Magnesium hydroxide is used for indigestion tablets/medicine as it neutralises stomach acid
• Calcium hydroxide is used in agriculture to neutralise acid soil
• Solubility of the group 2 sulfates decreases down the group. Calcium sulfate is sparingly soluble and barium sulfate is insoluble
• To confirm presence of Mg2+ ions you add aqueous sodium hydroxide to a solution of the group 2 compound. If Mg2+ ions are present, a thick white precipitate will be seen as magnesium hydroxide is sparingly soluble. (Mg2+(aq) + 2OH-(aq) -> Mg(OH)2(s)) If eg Ba2+ ions instead, colourless solution would be seen as barium hydroxide is much more soluble.
• To confirm presence of Ba2+ ions, sulfuric acid is added to a solution of the group 2 compound. If Ba2+ ions are present, a thick white precipitate would be seen as barium sulfate is insoluble. If eg Mg2+ ions are present instead, colourless solution would be seen at magnesium sulfate is soluble
• Barium salts are used to test for the presence of SO42-. To do this, add 1cm3 of HCl to 1cm3 of the sample being tested (to react with any CO32- that might be present as this will react with Ba2+ to also give white ppt). Then add 1cm3 BaCl2 and if a white precipitate is seen, SO42- must be present. (Ba2+(aq) + SO4–(aq) -> BaSO4(s)
• Barium salts are used in medicine for a barium meal, which is eaten before an x-ray as BaSO4 absorbs x-rays so can be used to visualise internal organs. Barium ions are toxic but the technique is harmless because the barium sulfate is insoluble so ions are not absorbed into the blood.
• Magnesium salts can be used to test for OH-. To do this, add 1cm3 of MgCl2(aq) to 1cm3 of sample being tested (no need to add HCl as MgCO3 is more soluble). If a white precipitate is seen this confirms the presence of OH-. (Mg2+(aq) +2OH-(aq) -> Mg(OH)2(s))
• Calcium oxide or calcium carbonate can be used to remove sulfur dioxide gas from flue gas (flue gas desulfurization). Either: CaO + SO2 -> CaSO3 (calcium sulfate (iv) or: CaCO3 + SO2 -> CaSO3 + CO2