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OCR A Jun 2009 Paper 1 Q2
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![This question compares the bonding, structure and properties of sodium and sodium oxide. (a) Sodium, Na, is a metallic element. Explain, with the aid of a labelled diagram, what is meant by the term metallic bonding.[3] (b) Sodium reacts with oxygen to form sodium oxide, Na2O, which is an ionic compound. (i) Write the equation for the reaction of sodium with oxygen to form sodium oxide.[1] (ii) State what is meant by the term ionic bond.[1] (iii) Draw a dot-and-cross diagram to show the bonding in Na2O. Show outer electrons only. [2]OCR 2009<br />
(c) Compare and explain the electrical conductivities of sodium and sodium oxide in the solid and liquid states.[5] [Total: 12]OCR 2009 Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_1_QP_JUN09_question_2-0.jpg)
![F321 Question 2 (a) Expected Answers + Mark Scheme Marks regular arrangement of labelled + ions with some attempt to show electrons (cid:57) scattering of labelled electrons between other species OR a statement anywhere of delocalised electrons (can be in text below) (cid:57) metallic bond as (electrostatic) attraction between the electrons and the positive ions (cid:57) (b) (i) (ii) 4 Na + O2 (cid:127)(cid:111) 2 Na2O OR 2 Na +O2 (cid:127)(cid:111) Na2O (cid:57) (electrostatic) attraction between oppositely charged ions(cid:57) June 2009 Additional Guidance Lattice must have at least 2 rows of positive ions If a metal ion is shown (e.g. Na+), it must have the correct charge ALLOW for labels: + ions, positive ions, cations If + is unlabelled in diagram, award the label for + from a statement of positive ions in text below DO NOT ALLOW as label or text positive atom OR protons OR nuclei ALLOW e OR e as label for electron DO NOT ALLOWas label for electron ALLOW correct multiples including fractions IGNORE state symbols<br />
F321 Question (iii) Expected Answers Mark Scheme Marks (c) Na shown with either 8 or 0 electrons AND O shown with 8 electrons with 6 crosses and 2 dots (or vice versa) (cid:57) Correct charges on both ions (cid:57) sodium is a (good) conductor because it has mobile electrons OR delocalised electrons OR electrons can move (cid:57) sodium oxide does not conduct as a solid (cid:57) sodium oxide conducts when it is a liquid (cid:57) ions cannot move in a solid (cid:57) ions can move OR are mobile when liquid (cid:57) Total June 2009 Additional Guidance For 1st mark, if 8 electrons shown around cation then extra electron(s) around anion must match symbol chosen for electrons in cation Shell circles not required IGNORE inner shell electrons ALLOW: 2[Na+] 2[Na]+ [Na+]2 (brackets not required) DO NOT ALLOW [Na2]2+ / [Na2]+ / [2Na]2+ DO NOT ALLOW: [Na2]2+ [Na2]+ [2Na]2+ [Na]2 + 12 Throughout this question, conducts and carries charge are treated as equivalent terms. DO NOT ALLOW free electrons for mobile electrons ALLOW poor conductor OR bad conductor Sodium oxide only conducts when liquid is insufficient to award solid conductivity mark ALLOW ions are fixed in place IGNORE electrons IGNORE charge carriers IGNORE delocalised ions or free ions for mobile ions Any mention of electrons moving is a CON<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_1_QP_JUN09_answer_2-0.jpg)
