AS Chemistry Exam Questions from OCR exam board: Electrons, bonding and structure Important Note: For students of CIE AS level, the syllabi are slightly different. Not everything you need to know is examined here. But these questions roughly map to CIE AS Chemistry topics 2, 3 and 9 1. Modern plasma television screens emit light when mixtures of noble gases, such as neon and xenon, are ionised. The first ionisation energies of neon and xenon are shown in the table below. element 1st ionisation energy / kJ mol –1 neon +2081 xenon +1170 Explain why xenon has a lower first ionisation energy than neon. ................................................................ ............................................................ ...... ................................................................ ............................................................ ...... ................................................................ ............................................................ ...... ................................................................ ............................................................ ...... ................................................................ ............................................................ ...... Patrick Brannac www. Smashing Science.org Page 1 of 78
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AS Chemistry Exam Questions from OCR exam board: Electrons, bonding and structureImportant Note: For students of CIE AS level, the syllabi are slightly different. Not everything you need to know is examined here.
But these questions roughly map to CIE AS Chemistry topics 2, 3 and 9
1. Modern plasma television screens emit light when mixtures of noble gases, such as neon and xenon, are ionised.
The first ionisation energies of neon and xenon are shown in the table below.
element1st ionisation energy
/ kJ mol–1
neon +2081
xenon +1170
Explain why xenon has a lower first ionisation energy than neon.
bond angle: ....................................................................................................[2]
(iv) A student investigated the conductivity of ammonium chloride.
She noticed that when the ammonium chloride was solid it did not conduct electricity. However, when ammonium chloride was dissolved in water, the resulting solution did conduct electricity.
(ii) ‘Dot-and-cross’ diagrams are used to model which electrons are present in the ion.
Draw a ‘dot-and-cross’ diagram, including outer electron shells only, to show the ions present in magnesium chloride, MgCl2.
[2]
(iii) A student finds that solid magnesium chloride and pure water do not conduct electricity. The student dissolved the magnesium chloride in the water and the resulting solution does conduct electricity.
20. The non-metals chlorine and carbon have very different boiling points. Chlorine is a gas at room temperature but carbon does not boil until well over 4500 °C.
Explain this difference, in terms of bonding and structure.
In your answer, you should use appropriate technical terms, spelled correctly.
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(a) An orbital is a region in which an electron may be found.
Draw diagrams to show the shape of an s orbital and of a p orbital.
s orbital p orbital
[2]
(b) Complete the table below to show how many electrons completely fill each of the following.
number of electrons
a d orbital
a p sub-shell
the third shell (n = 3)
[3]
(c) The energy diagram below is for the eight electrons in an oxygen atom. The diagram is incomplete as it only shows the two electrons in the 1s level.
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(i) adding labels for the other sub-shell levels,[1]
(ii) adding arrows to show how the other electrons are arranged.[1]
[Total 7 marks]
30. Successive ionisation energies provide evidence for the arrangement of electrons in atoms. The table below shows the eight successive ionisation energies of oxygen.
(iii) Draw a ‘dot-and-cross’ diagram for a molecule of H2O2. Show outer electrons only.
[2]
[Total 4 marks]
33. In water treatment plants, care must be taken as chlorine can react with nitrogen compounds to form the highly explosive compound, nitrogen trichloride, NCl3. Molecules of NCl3 have a bond angle of 107°.
35. In this question, one mark is available for the quality of spelling, punctuation and grammar.
Many physical properties can be explained in terms of bonding and structure. The table below shows the structures and some properties of sodium chloride and graphite in the solid state.
substance sodium chloride graphite
structure
electricalconductivity of solid
poor good
melting and boilingpoint
high high
solubility in water good insoluble
Explain these properties in terms of bonding and structure.[7]
Quality of Written Communication [1]
[Total 8 marks]
36. Magnesium exists naturally as a mixture of its isotopes, 24Mg, 25Mg and 26Mg.
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(ii) Molecules of NH3 are able to form hydrogen bonds. Draw a diagram to show the hydrogen bonding in ammonia. Include any relevant lone pairs and dipoles.
[2]
[Total 3 marks]
41. Describe and explain the density of ice compared with water.
42. In this question, you are provided with information about ionisation energies of elements. You are also provided with some additional information that will help you answer part (b).
44. In their reactions, calcium and strontium each lose electrons to form ions with a 2 charge. The first and second ionisation energies of calcium and strontium are shown below.
1st ionisation energy/ kJ mol–1
2nd ionisation energy/ kJ mol–1
calcium 590 1145
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45. Limestone contains the ionic compound, CaCO3. Limestone decomposes when it is heated strongly, forming an ionic compound, CaO and a covalent compound, CO2.
47. In this question, one mark is available for the quality of spelling, punctuation and grammar.
Many physical properties can be explained in terms of bonding and structure. The table below show some properties of elements in Period 2 of the Periodic Table.
element Li C(graphite)
N
electrical conductivityof solid good good poor
boiling point / C 1342 4000 –196
Explain these properties in terms of bonding and structure.[11]
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56. Reactions of the Group 2 metals involve removal of electrons. The electrons are removed more easily as the group is descended and this helps to explain the increasing trend in reactivity.
(i) The removal of one electron from each atom in 1 mole of gaseous radium atoms
is called the .....................................................................................................[2]
57. Iodine is extracted commercially from seawater with chlorine gas. Seawater contains very small quantities of dissolved iodide ions, which are oxidised to iodine by the chlorine gas.
(i) Write an ionic equation for the reaction that has taken place.
Nitrogen and oxygen are elements in Period 2 of the Periodic Table. The hydrogen compounds of oxygen and nitrogen, H2O and NH3, both form hydrogen bonds.
(i) Draw a diagram containing two H2O molecules to show what is meant by hydrogen bonding. On your diagram, show any lone pairs present and relevant dipoles.
[3]
(ii) State and explain two anomalous properties of water resulting from hydrogen bonding.
Mark Scheme1. Xe has a bigger atomic radius OR Xe has more shells
ALLOW Xe has more energy levelsALLOW Xe has electrons in higher energy levelALLOW Xe has electrons further from nucleusIGNORE Xe has more orbitals OR more sub-shellsDO NOT ALLOW ‘different shell’ or ‘new shell’
Xe has more shielding ALLOW More screeningThere must be a clear comparison ie more shielding OR increased shielding.i.e. DO NOT ALLOW Xe ‘has shielding’ALLOW Xe has more electron repulsion from inner shells
The nuclear attraction decreasesOR Outermost electrons of Xe experience less attraction (to nucleus)OR Increased shielding / distance outweighs the increased nuclear charge ORA throughout
ALLOW Xe has less nuclear pullIGNORE Xe has less effective nuclear chargeDO NOT ALLOW nuclear charge for nuclear attraction
[3]
2. (i) (Electrostatic) attraction between oppositely charged ions. IGNORE forceIGNORE references to transfer of electronsMUST be ions, not particles
1
(ii) Mg shown with either 8 of 0 electronsANDS shown with 8 electrons with 2 crosses and 6 dots (or vice versa)
Correct charges on both ions
M g S
2-2+
Mark charges on ions and electrons independentlyFor first mark, if 8 electrons are shown around the Mg then ‘extra electrons’ around S must match the symbol chosen for electrons around Mg Shell circles not requiredIGNORE inner shell electronsBrackets are not required
2
[3]
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3. (i) Electron pairs in covalent bonds shown correctly using dots andcrosses in a molecule of the F2O
Lone pairs correct on O and both F atoms
F F
O
Must be ‘dot-and-cross’circles for outer shells NOT neededIGNORE inner shellsNon-bonding electrons of O do not need to be shown as pairsNon-bonding electrons of F do not need to be shown as pairs
2
(ii) Predicted bond angle 104 – 105°. ALLOW 103 – 105° (103° is the actual bond angle)
There are 2 bonded pairs and 2 lone pairs Lone pairs repel more than bonded pairs
ALLOW responses equivalent to second marking point. e.g. There are 4 pairs of electrons and 2 of these are lone pairsALLOW ‘bonds’ for ‘bonded pairs’DO NOT ALLOW ‘atoms repel’DO NOT ALLOW electrons repelALLOW LP for ‘lone pair’ALLOW BP for bonded pairALLOW LP repel more if bonded pairs have already been mentioned
3
[5]
4. (i) (At least) two NH3 molecules with correct dipole shown with atleast one H with δ+ and one N with δ–
DO NOT ALLOW first mark for ammonia molecules with incorrect lone pairsDO NOT ALLOW first mark if H2O, NH2 or NH is shown
(Only) one hydrogen bond from N atom on one molecule to aH atom on another molecule
ALLOW hydrogen bond need not be labelled as long as it clear the bond type is different from the covalent N–H bondALLOW a line (i.e. looks like a covalent bond) as long as it is labelled ‘hydrogen bond)
Lone pair shown on the N atom and hydrogen bond must hitthe lone pair
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ALLOW 2-D diagramsALLOW two marks if water molecules are used. One awarded for a correct hydrogen bond and one for the involvement of lone pair
3
(ii) Liquid H2O is denser than solid In solid state H2O molecules are held apart by hydrogen bondsOR ice has an open lattice
ORAALLOW ice floats for first mark
ORH2O has a relatively high boiling point OR melting point
ALLOW higher melting OR boiling point than expectedDO NOT ALLOW H2O has a high melting / boiling point
(relatively strong) hydrogen bonds need to be brokenOR a lot of energy is needed to overcome hydrogen bondsOR hydrogen bonds are strong
ALLOW other properties caused by hydrogen bonding not mentioned within the specificationE.g. high surface tension – strong hydrogen bonds on the surface
2
[5]
5. 3d10 4s2 4p5
ALLOW 4s2 3d10 4p5
ALLOW subscripts or 3D10
ALLOW answers with 1s2 2s2 2p6 3s2 3p6 appearing twice[1]
6. Mg has a giant structure Metallic OR delocalised seen spelt correctly at least ONCE
Mg has metallic bonding OR description of metallic bonding as positive ionsand delocalised electrons
(There is electrostatic attraction between) positive ions and electrons DO NOT ALLOW as label nuclei OR protons for positive ionsALLOW labelled diagram of metallic bonding for second and third marks
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Lattice must have at least two rows of positive ions. If a Mg ion is shown it must correct chargeALLOW for labels: + ions, positive ions, cationsDO NOT ALLOW as label nuclei OR protons for positive ions
ALLOW e– or e as label for electronDO NOT ALLOW ‘–’ without label for electron
Cl has a simple molecular OR simple covalent (lattice) Covalent OR molecule OR molecular seen spelt correctly at least ONCEALLOW Cl is a (covalent) molecule
Cl has van der Waals’ forces (between molecules)ORCl has instantaneous dipole–induced dipolesORtemporary dipole–temporary dipole
IGNORE Cl has intermolecular bonding
van der Waals’ forces are weak and metallic bonds are strongORvan der Waals’ forces are weaker than metallic bondsORLess energy is needed to overcome van der Waals’ than metallic bonds
ALLOW ECF from incorrect descriptions of giant structure with strong bonds; e.g. Mg has giant ionic structureALLOW ECF from any incorrect intermolecular forcese.g. permanent dipole–dipole from marking point 5ALLOW vdW easier to breakORA
[6]
7. giant covalent (lattice)
layers
Each of the three properties below must be linked toexplanationgood conductor – because it has mobile electrons ORdelocalised electrons OR electrons can move
high melting / boiling point – because strong ORcovalent bonds have to be broken
soft – because there are van der Waals’ forces ORintermolecular forces OR weak bonds OR weak forcesbetween the layers
OR
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soft – because layers can slide Use annotations with ticks, crosses etc. for this part.All five marking points are independentALLOW giant atomic OR giant molecular ORmacromolecularALLOW planes OR sheetsAllow diagram showing at least two layersElectron(s) must be spelt correctly ONCEDO NOT ALLOW ‘strong ionic bonds’ OR strong metallicbonds.
[5]
8. (i) a shared pair of electrons ALLOW any response that communicates electron pairALLOW shared pairs
1
(ii)
H
H
HN
Must be ‘dot-and-cross’circles for outer shells NOT neededIGNORE inner shellsNon-bonding electrons of N do not need to be shown asa pair
1
(iii) Shape: pyramidal OR (trigonal) pyramid
Explanation:There are 3 bonded pairs and 1 lone pair Lone pairs repel more than bonded pairs
ALLOW ‘bonds’ for ‘bonded pairs’DO NOT ALLOW ‘atoms repel’DO NOT ALLOW electrons repelALLOW LP for ‘lone pair’ALLOW BP for bonded pair
3
[5]
9. (i) 1s22s22p63s23p6 ALLOW subscripts
1
(ii)
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‘Dot-and-cross’ diagram to show four shared pairs ofelectrons one of which is a dative covalent bond (whichmust consist of the same symbols)
IGNORE inner shellsIGNORE ‘+’ sign BUT DO NOT ALLOW a ‘−’ sign.Brackets and circles not required
1
(iii) tetrahedral
109.5° ALLOW 109 – 110°
2
(iv) ions OR electrons cannot move in a solid
ions can move OR are mobile in solution ALLOW ions can move in liquidDO NOT ALLOW ions can move when moltenALLOW 1 mark for:‘Ions can only move in solution’
2
[6]
10.
regular arrangement of labelled + ions with some attemptto show electrons
scattering of labelled electrons between other speciesORa statement anywhere of delocalised electrons (can be intext below)
metallic bond as (electrostatic) attraction between theelectrons and the positive ions
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Lattice must have at least 2 rows of positive ionsIf a metal ion is shown (e.g. Na+), it must have the correct chargeALLOW for labels: + ions, positive ions, cationsIf ‘+’ is unlabelled in diagram, award the label for ‘+’ from a statement of ‘positive ions’ in text belowDO NOT ALLOW as label or text positive atom OR protons OR nuclei
ALLOW e– OR e as label for electronDO NOT ALLOW ‘–’ as label for electron
[3]
11. (i) 4 Na + O2 → 2 Na2O
OR 2 Na + ½ O2 → Na2O ALLOW correct multiples including fractionsIGNORE state symbols
1
(ii) (electrostatic) attraction between oppositely charged ions1
(iii)
N a
N a
O+
+2 –
Na shown with either 8 or 0 electronsANDO shown with 8 electrons with 6 crosses and 2 dots (orvice versa) Correct charges on both ions
For 1st mark, if 8 electrons shown around cation then‘extra’ electron(s) around anion must match symbolchosen for electrons in cationShell circles not requiredIGNORE 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+
2
[4]
12. sodium is a (good) conductor because it has mobile
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electrons OR delocalised electronsOR electrons can move
sodium oxide does not conduct as a solid
sodium oxide conducts when it is a liquid
ions cannot move in a solid
ions can move OR are mobile when liquid Throughout this question, ‘conducts’ and ‘carries charge’ are treated as equivalent terms.DO NOT ALLOW ‘free electrons’ for mobile electronsALLOW poor conductor OR bad conductor‘Sodium oxide only conducts when liquid’ is insufficient to award ‘solid conductivity’ markALLOW ions are fixed in placeIGNORE electronsIGNORE charge carriersIGNORE ‘delocalised ions’ or ‘free ions’ for mobile ionsAny mention of electrons moving is a CON
[5]
13. the energy required to remove one electron from eachatom in one mole of gaseous atoms
ALLOW 3 marks for:the energy required to remove one mole of electrons from one mole of atoms atoms in the gaseous state If no definition, ALLOW one mark for the equation below, including state symbols.X(g) → X+(g) + e– / X(g) – e– → X+(g)ALLOW e for electronIGNORE state symbol for electron
[3]
14. (i) O+(g) → O2+(g) + e– answer must have state symbolsALLOW e for electronALLOW O+(g) – e- → O2+(g)DO NOT ALLOW O+(g) + e– → O2+(g) + 2e–
IGNORE state symbol for electron1
(ii) the O+ ion, is smaller than the O atomORthe electron repulsion/shielding is smallerORthe proton : electron ratio in the 2+ ion is greater than inthe 1+ ion
ALLOW the outer electrons in an O+ ion are closer to the
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nucleus than an O atomDO NOT ALLOW ‘removed from next shell down’
1
[2]
15. (i) number of protons (in the nucleus) ALLOW proton numberALLOW number of protons in an atomIGNORE reference to electrons
1
(ii) (1s2)2s22p63s23p63d24s2 ALLOW 1s2 written twiceALLOW subscriptsALLOW 4s2 before 3d2+
1
(iii) Mn / manganese and d ALLOW D
1
[3]
16. (i)
δ+ δ+
δ + δ +
H O H
H H
Oδ -δ +
H y dro g en b on d
Shape of water with at least one H with δ+ and at least oneO with δ–
H-bond between H in one water molecule and a lone pairof an O in another water molecule
hydrogen bond labelledOR H2O has hydrogen bonding
all marks can be awarded from a labelled diagramIf HO2 shown then DO NOT ALLOW 1st markDipole could be described in words so it does not need to be part of diagram.At least one hydrogen bond must clearly hit a lone pairLone pair interaction could be described in words so it does not need to be part of diagram.DO NOT ALLOW hydrogen bonding if described in context of intramolecular bonding, ie
HO
H
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(ii) no hydrogen bondingORweaker intermolecular forces
DO NOT ALLOW ‘weaker’/ ‘weak’ hydrogen bondingALLOW weaker van der Waals’ forcesALLOW weaker dipole-dipole interactionsDO NOT ALLOW ‘weak intermolecular forces’(ie comparison essential here)DO NOT ALLOW ‘no intermolecular forces’
1
[4]
17. (i) atoms of the same element with different numbers ofneutrons/different masses (1) 1
positive ions (1) electrons (1) (must be labelled) 2
(ii) the electrons move (1) 1[3]
19. (i) attraction between oppositely charged ions 1
(ii)
C l
M g-
C l
-
Mg and Cl both with 8 electrons in outer shell, (accept 0 electrons for Mg)Cl must have one dot to seven crosses or vice versa (1)correct charges on each ion (1) 2
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(iii) MgCl2 does not conduct when solid because ions are fixed in lattice (1)H2O does not conduct as there are no free charge carriers/watermolecules are uncharged (1)MgCl2 conducts when aqueous because ions are free to move (1) 3
[6]
20. To boil Cl2, van der Waals’ forces/intermolecular forces are broken(with van der Waals/intermolecular spelt correctly) (1)To boil C, covalent bonds are broken (1)covalent bonds are stronger than van der Waals’ forces (1)
[3]
21. (i) H2O NH32 3 (1)2 1 (1) 2
(ii)
N H
H
H 1 0 7 º
shape (1) bond angle labelled on diagram as 107° (1)
120º
S O O
shape (1) bond angle labelled on diagram as 110–120° (1) 4[6]
22. H bonding from lone pair on O of 1 H2O molecule to H of another (1)dipoles shown (1)
Two properties:Ice is lighter than water/ max density at 4°C (1)explanation: H bonds hold H2O molecules apart
/ open lattice in ice/ H-bonds are longer (1)
Higher melting/boiling point than expected (1)explanation: strength of H bonds that need to be broken (1)
must imply that intermolecular bonds are broken
High surface tension/viscosity (1)explanation: strength of H bonds across surface (1)
[6]
23. (i) 1s22s22p63s23p6 1
(ii) 3 1
(iii) 10 1
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(iv) ‘dot-and-cross’ of Ca2+ with either 8 electrons or noelectrons. ‘dot-and-cross’ of 2OH– correct 2N.B. H electron and Ca electrons can look the same.
[5]
24. (i) attraction between oppositely charges ions 1
(ii) shared pair of electrons 2‘shared electrons’ scores 1 mark only
[3]
25. (i) attraction of an atom/element for electrons in a (covalent) bond/bonded pair 2
(ii) one element attracts bonded pair more/is more electronegative than other
– on more electronegative atom and on less 2
electronegative element in example
May need to look for these marks below if not given here.[4]
26. H–bond shown between H of one molecule and O, N or F ofanother H-bond shown going to a lone pair
[2]
27. (a) 3
element structure bonding
Mg giant metallic Si giant covalent S simple covalent
1 mark for each correct row
(b) Si has strong forces between atoms/covalent bonds are broken P has weak forces between molecules/intermolecular forces/van der Waals’ forces are broken 2
(c) From Na Al, no of delocalised electrons increases charge on positive ion increases/ionic size decreases/charge density increases attraction between ions and electrons increases/metallic bonding gets stronger 2
[7]
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(iii) = 24.33 (calc value: 24.3269. This scores one mark)24.32 with no working, award 1 mark only.24.3 with no working, no marks (Periodic Table value) 2
[5]
37. (i)
positive ions electrons (must be labelled)If Mg2+ shown then must be correct: Mg+ not worthy 2
(ii) electrons move 1[3]
38. (i) Oxidation state goes from 0 in O2 2 in MgO 2
(ii)
M g
2+ 2–
or with Mg full shell.correct dot and cross ; correct charges 2
[4]
39. (i) mark vertically:
H2O NH3
2 3
2 1 2
3D Diagram required or diagram with name
(ii) labelled bond angle requiredNH3 pyramidal molecule shown 107 (106-108)SO2 non-linear molecule shown 110 – 130 4
[6]
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40. (i) oxygen/ nitrogen is more electronegative/molecule has atoms with different electronegativities/oxygen/more electronegative atom … attracts bondedelectron pair more 1
(ii) H bonding from N of 1 NH3 molecule to H of another NH3
molecule with a Hδ+ shown and a Nδ– shownwith lone pair involved in bond2nd mark is available from water molecule(s) 2
[3]
41. ice is less dense than water
hydrogen bonds hold H2O molecules apart in ice /hydrogen bonds cause an open lattice structure 2
[2]
42. (a) Energy change when each atom in 1 moleof gaseous atomsloses an electron (to form 1 mole of gaseous 1 ions). 3
(b) From Li N, ionisation energy increasesnumber of protons/nuclear charge increasesnuclear attraction increases / shell drawn in by increasednuclear charge/ atomic radius decreasesacross period, electrons added to same shell
Not same subshellFrom Be B, ionisation energy decreasesfor B, electron is removed from a p sub-shell/porbital/different sub-shellwhich has a higher energy 7
watch for distinction between nuclear attraction andnuclear charge in candidates’ scripts.Also watch for confusion between shell and subshell.
AlSharp rise in successive ionisation energy between 3rd and4th IEmarking a change to a new or different shell / there are 3electrons in the outer shell 3
mention of ‘orbital’ or ‘sub-shell cancels ‘shell mark’ Each marking point for Al is independent
QoWC: links together two pieces of informationcorrectly within two of the sections below:1. General trend across period2. Be to BSuccessive ionisation energies
[13]
43. (i) 107 (accept any angle in the range 108 91) 1
(ii) electron pairs repel electron pairs/bonds go as far apart as possible
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Equation with correct charges and 1 electron lost state symbols ‘−’ not required on ‘e’ 2
(ii) same number of protons or same nuclear charge attractingless electrons/electron removed from an ion/less electron-electron repulsion (not less shielding)/ion is smaller 1
(iii) atomic radii of Sr > atomic radii of Ca/Sr has electrons in shell further from nucleus than Ca/Sr has electrons in a higher energy level/Sr has more shells Therefore less attraction Sr has more shielding than Ca (‘more’ is essential) 3
increased nuclear charge is outweighed / despite increased nuclearcharge …..by at least one of the factors above
[6]
45. attraction between oppositely charged ions/
oppositely charged atoms 1
For CaO: correct dot and cross ; correct charges
For CO2: correct dot and cross 3
1s22s22p63s23p6 1[5]
46. (i) dative covalent, bonded pair comes from same atom/ 1electron pair is donated from one atom/both electrons are from the same atom
(ii) Ca(NO3)2 CaO 2NO2 ½O2 or double equation with 2/2/4/1 1
[2]
47. High boiling point or difficult to break linked to strong bonds in the rightcontext within Li or C 1
Li conducts by delocalised/free/mobile electrons structure: giant metallic
or ‘ ions with a sea of electrons’ for giant mark
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(must be ‘dot AND cross’ or electron source clearly shown(different coloured for source?)
[2]
50. correct dot and crosses correct charges
[2]
51. (i) Energy change when each atom in 1 mole of gaseous atoms loses an electron (to form 1 mole of gaseous 1 ions). 3
(ii) increasing nuclear charge/number of protons electrons experience greater attraction or pull / atomicradius decreases / electrons added to same shell /same orsimilar shielding 2
(iii) In B, electron being removed is at a higher energy /In Be, electron being removed is at a lower energy
An s electron is lost in Be AND a p electron is lost in B 2[7]
52. uneven distribution of electrons instantaneous /oscillating/changing/temporary/transient/dipole on one atom causes an induced/resultant dipole on anothermolecule/atom
chlorine gas; bromine liquid; iodine solid/volatility decreases from Cl2 Br2 I2/boiling point increases from Cl2 Br2 I2/
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