OCR A Jun 2012 Paper 1 Q2 (with explained solutions) |

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OCR A Jun 2012 Paper 1 Q2

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2 Chemists can use the Periodic Table to predict the behaviour of elements. (a) What is the name of the term used to describe the repeating patterns in the Periodic Table?[1] (b) Melting points show a trend across a period. The table below shows the melting points of three elements in Period 3 of the Periodic Table. element aluminium silicon phosphorus melting point / C 660 1410 44 Explain the trend shown in terms of bonding and structure. In your answer, you should use appropriate technical terms spelled correctly.[6]OCR 2012<br />
(c) Scientists use sketch graphs to show trends. (i) Draw a sketch graph to show the general trend in ionisation energy across Period 3. ionisation energy Na Mg Al Si Cl Ar [1] (ii) Draw a sketch graph to show the general trend in atomic radius across Period 3. atomic radius Na Mg Al Si Cl Ar [1] [Total: 9]OCR 2012 Turn over<br />

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F321 Question 2 (a) (b) Mark Scheme June 2012 Answer Periodicity (cid:57) Al bonding mark Al has metallic (bonding) OR has (electrostatic) attraction between positive ions and (delocalised) electrons (cid:57) Si bonding mark Si has covalent (bonding) OR has shared pairs of electrons between atoms (cid:57) P bonding mark P has induced dipoles OR has van der Waals forces (between molecules) (cid:57) Structure mark 1 Al AND Si are Giant (cid:57) Structure mark 2 P is Simple molecular OR simple covalent (cid:57) Bond strength mark Metallic AND covalent are stronger than vdWs OR Bonds broken in Al AND in Si are stronger than the forces broken in P OR More energy is needed to overcome bonds in Al AND Si than the forces in P (cid:57) Marks Guidance ALLOW phonetic versions Use annotations with ticks, crosses, ECF etc for this part DO NOT ALLOW marking point 1 if Al has dipoles OR intermolecular forces OR molecules OR atoms OR attraction between nuclei and electrons OR attraction between oppositely charged ions DO NOT ALLOW marking point 2 if Si has dipoles OR intermolecular forces OR molecules but IGNORE molecule Must be induced dipoles ALLOW vdW for van der Waals IGNORE P has covalent bonds for marking point 3 Quality of Written Communication: giant spelled correctly once and used in context for the fourth marking point DO NOT ALLOW covalent bonds are broken in phosphorus for marking point 6, but ALLOW answers that inform Al and Si are stronger than P, ignoring incorrect forces or bonds used above IGNORE heat but ALLOW heat energy<br />
F321 Mark Scheme June 2012 Question (i) (c) Increasing straight line OR curve from Na to Ar (cid:57) Answer Marks (ii) Decreasing straight line OR curve from Na to Ar (cid:57) Guidance ALLOW bar charts OR points IGNORE the standard of drawing as long as the trend is clear IGNORE decrease between Mg/Al and P/S Essentially the mark is for Na < Mg < Si < P < Cl < Ar AND Al < Si AND S< Cl ALLOW bar charts OR points IGNORE the standard of drawing as long as the trend is clear IGNORE Ar Essentially the mark is for Na > Mg > Al > Si > P > S > Cl Total<br />

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