AQA A-Level Chemistry - Periodicity with correct answers

Periodicity pattern in change of properties in a row of elements and this pattern is repeated in the next row Block S block - the block that belongs to hydrogen and groups 1 and 2 p block - The block that belongs to the non-metals and metalloids d block - The block that belongs to the transition metals f block - The block that belongs to the lanthanides and actinides elements in each block have their highest energy electron in that sub-shell position in the periodic table is determined by its proton number 00:01 01:36 Physical properties of period 3 elements Atomic radius trend - increases - increase in no. of protons - increased nuclear charge - increased force of attraction on e- - similar shielding - atomic radius decreases First ionisation energy - increases but drop between Mg and Al and drop between P and S Melting point of elements - Na - Al - increases - smaller ion -increased nuclear charge - stronger electrostatic force of attraction Silicon - macromolecular - many strong colavlent bonds must be broken - peak P-Ar - depends on size P4, S8, Cl2 and Ar Larger the molecule - stronger Van der Waals between the molecules - more energy required to overcome the forces N.B - Argon - small and single atoms with e- close to nucleus - cannot be polarised - electron cloud not easily distorted Physical properties of Group 2 elements Atomic radius - increases - extra shell - increased shielding - despite increase in nuclear charge First ionisation energy - increased shell - increased nuclear distance - increased shielding - despite increase in nuclear charge Melting point - decreases - increase in ion size - more shells - weaker electrostatic force of attraction - but blip in Mg due to a unique crystal structure The reactions of Mg-Ba with water produces X(OH)2 reactivity increases down the group Atom gets larger - outershell e- furthe away from nucleus e- more readily lost OH- ions formed Mg has lowest reactivity so might have to use steam Solubilities Solubility of hydroxides increase down the group So more OH- ions formed down the group So solutions are more alkaline as you go down the group Mg(OH)2 is sparingly soluble Solubility of sulphates decrease down the group. BaSO4 is insoluble. Test the solubilities of group 2 hydroxides by mixing a soluble group 2 salt eg X(NO3)2 with NaOH. Test the solubilities o f group 2 sulfates by mixing solutions of soluble group 2 salts eg X(NO3)2 with H2SO4 The use of magnesium in Titanium extraction TiO2 (Titanium ore) converted to TiCl4 by heating with carbon in a steam of chlorine gas. It is difficult to extract from its ore because Titanium reacts with carbon to form Titanium carbide TiC. The TiCl4 is then purified using distillation and then reduced by Magnesium at 1000C It is quite expensive Other used of group 2 compounds Mg(OH)2 in medicine - antacid - reacts with excess acid in the body relieves digestion Barium meals - insoluble so forms a suspension - soft tissue does not show up on X-ray but BaSO4 is insoluble and can be used to view organ structures. Other Ba compunds can't be used because Ba2+ ions are poisonous. Ca(OH)2 in agriculture - neutralising acidic soils in agriculture