Bonding Answers - Science Skool!

Bonding Answers

Chemistry - AQA GCE Mark Scheme 2010 June seriesQuPartSubPartMarking GuidanceMark1aishared pair of electrons1Can have one electron from each atom contributes to the bondNot both electrons from one atom1aii13Cl2 F2 221OnlyIgnore state symbols even if wrong1b1Allow any structure with 4 bpClF3FFCCommentsWatch for Cl in centre- it must be CIgnore wrong bond anglesClClRepresentations of lone pairs allowed are the two examples shown withor without the electrons in the lobe.Also they can show the lone pair for either structure by two crosses/dots or a line with two crosses/dots on it e.g.FFFFClFORCl1FxxFClxxcDipole – dipole13FFClFOr a structure with 3 bp and 2 lp1xxF OrxxFAllow van der Waals/ vdw/ London/ dispersion/ temporary dipole induced dipoleNot dipole alone

Chemistry - AQA GCE Mark Scheme 2010 June series1d1d1eiiiCoordinate/ dative (covalent)1If wrong CE 0/3 but if ‘covalent’ or left top line blank, mark on.(Lone) pair of electrons/ both electrons (on F-)1CE if lone pair is from BDonated from F / fluoride or donated to the BF31Must have the – sign on the F ie FIgnore FlM3 dependent on M2109 to 109.51238 x 1004381For 1 mark allow 238 as numerator and 438 as denominator or correctstrings 54.3%12 marks if correct answer to 3 sig figs.54% or greater than 3 sig figs 1 mark4

Chemistry - AQA GCE Mark Scheme 2010 June seriesQuPart7a57b55577cdSubPartMarking GuidanceMarkPart Sub Marking GuidanceIodine – molecularParta1CommentsMarkCommentsNot covalent latticeGraphite- macromolecular/giant covalent/giant atomic1Layers of (C atoms)1If any other element mentioned other than C, CE 0Connected by covalent bonds within each layer1Ignore the no of covalent bonds around the C if mentionedThe first 3 marks could be scored with a labelled diagram.Need to label or state covalent bonds within the layers.Covalent or ionic or metallic bonds between molecules CE 0b Van der Waals forces/ IMF between layers/ weak forcesbetween layerscMany/strong covalent bonds need to be brokendVan der Waals forces are weak or easily broken111Not vdw between atomsVan der Waals between molecules (or implied)1Allow weak IMF 2Does not have delocalised/free electrons1Only allow answer with respect to iodineNot all electrons used in bondingIgnore free ions11

Chemistry - AQA GCE Mark Scheme 2010 January seriesQuestion Part Sub Marking GuidancePart33(a)MarkCommentsHydrogen/H bonds1Not just hydrogenvan der Waals/vdw/ dipole-dipole/London/temporarily induceddipole/dispersion forces1Not just dipole3M1 for partial charges as indicatedin diagram (correct minimum)M2 for all four lone pairsM3 for H bond from the lp to the H(δ ) on the other moleculeLone pair on hydrogen CE 0OHO CE 0If only one molecule of water shownCE 01Ignore energy referencesComparison must be stated orimplied(b)OHH3(c)OHδ δ-HHydrogen bonds/IMF (in water) strongerORIMF / VDW / dipole-dipole forces (in H2S) are weakerORH bonding is the strongest IMF3(d)Atoms/molecules get larger/more shells/more electrons/ more 1surface areaNot heavier/greater Mrtherefore increased Van der Waals/IMF forcesIgnore references to dipole-dipoleforces17

Chemistry - AQA GCE Mark Scheme 2010 January series33(e)(f)Dative (covalent)/ coordinate1If not dative/coordinate CE 0/2If covalent or blank read on(Lone) pair/both electrons/two electrons on O(H2) donated (to H )OR pair/both electrons come from O(H2)1Explanation of a coordinate bondspecific to oxygen or water requiredNot just H attracted to lone pairsince that is nearer to a H bondionic1if not ionic CE 0oppositely charged ions / and – ions or particles1ions attract strongly OR strong/many (ionic) bonds must be broken1atoms or molecules loses M2 andM3S- loses M2Reference to IMF loses M2 and M38

Chemistry - AQA GCE Mark Scheme 2010 January seriesQuestionPart SubPartMarking Guidance6FFAsMarkComments1Mark M1 – M5 independentlyM1 for 5 bond pairs around AsDo not penalise A for As or Fl for F1Allow trigonal dipyramid1M3 for 2 bond pairs to F and 2 lonepairsLone pairs can be shown as lobeswith or without electrons or as xx orFF Ftrigonal / triangular bipyramid(al)ClFFxxBent / V shape / non-linear / triangular / angular1104 - 106 1Bent-linear contradictionDo not allow trigonal(For candidates who thought this was CIF2 which containediodine allowFICFNot just triangularTrigonal / triangular planar120 12

Mark Scheme – General Certificate of Education (A-level) Chemistry – Unit 1: Foundation Chemistry – June 2011Question3(a)Marking GuidanceMarkIodine has more electrons / iodine is bigger (atom ormolecule) / iodine has bigger Mr / bigger surface areaComments1Stronger / more van der Waals forces / vdw / London /temporarily induced dipole / dispersion forces betweenmolecules1Stronger VdW intermolecular forces M2If stated VdW between atoms lose M23(b)(i)1Mark is for 3 bp and 1 lp attached to N (irrespective of shape)1Mark is for 3 bp and 0 lp attached to B (irrespective of shape)1Accept tetrahedral / triangular pyramid1Not triangular or triangular planar1071Allow 106-108Hydrogen bonds1Allow H-BondsNFFHFBFFNHF2 shape - pyramidal / trigonal pyramidBF3 shape3(b)(ii)3(c)- trigonal planarNot just HydrogenApply list principle eg Hydrogen bonding and dipole-dipole 07

Mark Scheme – General Certificate of Education (A-level) Chemistry – Unit 1: Foundation Chemistry – June 20113(d)Coordinate / dative covalent / dative1If covalent mark onIf ionic / metallic CE 0Lone pair / both electrons/ 2 electrons on N(HF2) donated(to BF3)18Direction of donation needed here

Mark Scheme – General Certificate of Education (A-level) Chemistry – Unit 1: Foundation Chemistry – June 2011Question4(a)(i)Marking GuidanceMarkMetallic4(a)(ii)Comments1Allow body centred cubic1One mark for regular arrangement of particles. Can have aspace between them Do not allow hexagonal arrangementOR1 One mark for in eachIgnore electronsNa Na Na Na Na Na If it looks like ionic bonding then CE 0/24(b)(i)Ionic1CE 0 for 4(b)(i) and 4(b)(ii) if not ionic4(b)(ii)Strong (electrostatic) attraction1Any mention of IMF or molecules / metallic / covalent in 4(b)(ii)then CE 0/2Between oppositely charged ions / particles1Or and – ionsIodide / I– bigger (ion) (so less attraction to the Na ion)1Need comparison4(c)Do not allow iodine is a bigger atomIgnore I- has one more e- shellCE 0 if IMF / covalent / metallic mentioned9

Mark Scheme – General Certificate of Education (A-level) Chemistry – Unit 1: Foundation Chemistry – January 2011QuestionMarking GuidanceMark1(a)Water or H2O or molecules (in ice) are held further apart(than in liquid water)/(more) space/gaps/holes in structure/Water or H2O or molecules (in ice) are more spread out1CommentsAllow water (liquid) is more compact / lessspace/gaps/holesCE if holes filled with air, O2 etcCE if macromoleculeCE if atoms further apart (since ambiguous)Ignore spaces filled with H2OIgnore reference to H bondsAllow better tessellation in liquid water1(b)(i)Hydrogen bonding1Allow H bondsDo not allow „hydrogen‟ only but mark on1(b)(ii)Van der Waals‟ / VdW1Allow London forces, dispersion forces, temporary induceddipole forces1(b)(iii)Hydrogen bonding is stronger (than van der Waals forces)/ IMF in ice stronger (than IMF in methane)/ H bonds takemore energy to break1Not H Bonds are strong (needs comparison)If (b)(i) OR (ii) is incorrect, cannot award (b)(iii)If (b)(i) and /or (ii) is blank, can score (b)(iii)3

Mark Scheme – General Certificate of Education (A-level) Chemistry – Unit 1: Foundation Chemistry – January 20111(c)(i)Structure showing 3 bonds to H and 1 lone pair1do not insist on the sign(trigonal) pyramid(al) /(distorted) tetrahedral1Allow triangular pyramidNot square pyramidIgnore bond angles in structureM2 independent of M11(c)(ii)1107Allow range106 - 108Ignore (C)1(c)(iii)1(d)NH3 /ammonia1Contradictions (eg NH4 ammonia) CE 031Allow three/ III/ 3 lone pairs/ 3lp/ 3 lone pairs of electrons4

Mark Scheme – General Certificate of Education (A-level) Chemistry – Unit 1: Foundation Chemistry – June 2012QuestionMarking GuidanceMark3(a)Comments1Need to see 3 P-H bonds and one lone pair (ignore shape).Coordinate / dative1If not coordinate / dative then chemical error CE 0 unless blankor covalent then M1 0 and mark on.Pair of electrons on P(H3) donated (to H )1Do not allow a generic description of a coordinate bond.3(c)109.5 / 109½ / 109 28’1Allow answers in range between 109 to 109.5 3(d)Difference in electronegativity between P and H is toosmall1Allow P not very electronegative / P not as electronegative as N,O and F / P not electronegative enough / P not one of the 3 mostelectronegative elements.Do not allow phosphine is not very electronegative.PHH3(b)H7

Mark Scheme – General Certificate of Education (A-level) Chemistry – Unit 1: Foundation Chemistry – June 2012QuestionMarking GuidanceMarkComments4(a)(i)Macromolecular / giant covalent / giant molecular / giantatomic14(a)(ii)Delocalised electrons / free electrons1Able to move / flow (through the crystal)1Covalent bonds1Many /strong / hard to break / need a lot of energy tobreak1M2 dependent on M1.Ignore van der Waals’ forces.4(b)(i)(Giant) metallic / metal (lattice)1If FCC or BCC or HCP or giant or lattice, mark on.If incorrect 4(b)(i), chemical error CE for 4(b)(ii) and 4(c)(ii).4(b)(ii)Nucleus / protons / positive ions and delocalisedelectrons (are attracted)1QWC Must be delocalised electrons – not just electrons.Chemical error 0/2 for 4(b)(ii) if other types of bonding or IMFmentioned.Strong attraction1Allow strong metallic bonding for one mark if M1 and M2 are notawarded.Layers of atoms/ions slide (over one another)1Do not allow just layers.4(a)(iii)4(c)(i)8If covalent, molecular, giant, lattice, hexagonal or blank mark on.If metallic, ionic or IMF chemical error CE 0 for 4(a)(i), 4(a)(ii)and 4(a)(iii).Allow M2 for electrons can move / flow.Ignore electrons can carry a current / charge.

Mark Scheme – General Certificate of Education (A-level) Chemistry – Unit 1: Foundation Chemistry – June 20124(c)(ii)4(d)(Strong) (metallic) bonding re-formed / same (metallic)bonding / retains same (crystal) structure / same bondstrength / same attraction between protons anddelocalised electrons as before being hammered orwords to that effect1If IMF, molecules, chemical error CE 0/1 for 4(c)(ii).If metallic not mentioned in 4(b)(i) or 4(b)(ii) it must be mentionedhere in 4(c)(ii) to gain this mark.Do not allow metallic bonds broken alone.Ignore same shape or same strength.(giant) Ionic1If not ionic, chemical error CE 0/3Between and – ions / oppositely charged ions or Mg2 and O2-1If molecules mentioned in explanation lose M2 and M3Allow one mark for a strong attraction between incorrect chargeson the ions.Strong attraction19

Mark Scheme – General Certificate of Education (A-level) Chemistry – Unit 1: Foundation Chemistry – January 2012Question1(a)Marking GuidanceMarkCovalent1CommentsIf not covalent CE 0/2If dative covalent CE 0/2If blank mark onIgnore polarIf number of pairs of electrons specified, must be 3Shared pair(s) of electrons / one electron from Br and oneelectron from F1(b)(i)1Not 2 electrons from 1 atomNot shared pair between ions/moleculesF1FBrFBrFFBrF3 should have 3 bp and 2 lp and correct atoms for themarkPenalise FlorF1BrF3 if trigonal planar shown 120 Allow 84 - 90 or 120 and ignore 180 Irrespective of shape drawnor if T shape shown 84 - 90 3