OCR A Jun 2015 Paper 1 Q6 (with explained solutions) |

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OCR A Jun 2015 Paper 1 Q6

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This question is about the attraction between particles. 14 (a) State how and explain why the attraction between nuclei and outermost electrons in gaseous atoms varies across Period 3.[2] (b) The table shows the boiling points of ammonia, fluorine and bromine. ammonia, NH3 fluorine, F2 bromine, Br2 Boiling point / C33188 59 Explain the different boiling points of NH3, F2 and Br2. Include the names of any relevant forces and particles. In your answer you should use appropriate technical terms, spelled correctly.OCR 2015<br />
15[5] [Total: 7] END OF QUESTION PAPEROCR 2015<br />

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F321 Question 6 (a) Mark Scheme June 2015 Mark Guidance ALLOW There is no change in shielding But DO NOT ALLOW there is no shielding DO NOT ALLOW electrons are at the same distance Answer The attraction (between nuclei and outermost electrons) increases (across the period) AND The nuclear charge increases OR The number of protons increase (cid:57) (Outer) electrons are in the same shell OR (Outer) electrons experience similar shielding OR Same number of shells OR Atomic radius decreases (cid:57) 12<br />
F321 Question (b) Mark Scheme June 2015 Answer M1 NH3 forces mark NH3 has hydrogen bonding (cid:57) M2 F2 AND Br2 forces mark F2 AND Br2 have van der Waals (forces) (cid:57) M3 Type of particle mark Forces OR attractions are between molecules OR are intermolecular for ammonia AND Forces OR attractions are between molecules OR are intermolecular for fluorine OR for bromine (cid:57) Mark Guidance Quality of written communication: molecule(s) or intermolecular spelled correctly once and used in context for the third marking point. ALLOW H-bonding for hydrogen bonding IGNORE van der Waals forces AND permanent dipoles in M1 IGNORE covalent bonds for M1 AND M2 ALLOW, for van der Waals: vdWs OR induced dipole temporary OR instantaneous dipole (-dipole) forces ALLOW for forces: attractions OR interactions; DO NOT ALLOW M3, M4 or M5 if covalent OR ionic bonds are the forces between the particles in that mark M3 can be seen anywhere eg in M1 NH3 has hydrogen bonding between molecules AND the intermolecular force in Br2 is stronger than that of F2 eg a generic statement such as boiling point of these substances is determined by strength of intermolecular bonding eg All these molecules are held together by weak forces 13<br />
June 2015 Guidance If correct force is given in M2 ALLOW, for M4, intermolecular force in Br2 is stronger than that in F2 ALLOW more van der Waals for greater van der Waals ALLOW more shells of electrons IGNORE permanent dipoles in NH3 for M5 if quoted in addition to hydrogen bonding If correct force is given in M1 AND M2 ALLOW, for M5, intermolecular force in Br2 is stronger than that in NH3 AND intermolecular force in NH3 is stronger than that in F2 If incorrect intermolecular force is given in M1 OR M2 ALLOW this as ECF for M5 but DO NOT ALLOW if the comparison is based only on van der Waals forces Eg DO NOT ALLOW the van der Waals forces in bromine are stronger than those in ammonia which in turn are stronger than those in fluorine F321 Question Answer Mark Scheme Mark M4 Br2 / F2 comparison mark The van der Waals forces in Br2 are greater than in F2 AND Because bromine has more electrons than fluorine (cid:57) M5 Br2 / NH3 / F2 comparison mark The van der Waals forces in Br2 are greater than hydrogen bonding in NH3 AND hydrogen bonding in NH3 is stronger than van der Waals forces in F2 (cid:57) Total 14<br />

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