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SOLUCIONARIO ESTRUCTURA ATÓMICA 2009/10/11 1. C

2. (a)argon has a greater proportion of heavier isotopes / OWTTE / argon has a greater number of neutrons; 1

(b) 19 protons and 18 electrons; 1

(c) 2, 8, 8; 1

Accept 1s2 2s2 2p6 3s2 3p6.

3. 2809 = 3.10 × 30 + 28x + 29(96.9 – x);

% 28Si = (93 + 2810.1 – 2809) = 94.1 %; 2

Award [2] for correct final answer.

4. 14C and radiocarbon dating/(tracer in) medical/scientific tests;

11C and (tracer in) medical/scientific tests; 1 max

5. B

6. B

7. (a) cobalt has a greater proportion of heavier isotopes / OWTTE /

cobalt has greater number of neutrons; 1

(b) 27 protons and 25 electrons; 1

(c) 1s22s22p63s23p63d7 / [Ar] 3d7; 1

(d) 60Co/Co-60/cobalt-60 and radiotherapy/sterilization of medical supplies/radiation treatment of food sterilizations/industrial

radiography/density measurements in industry/(medical/radioactive) tracer;

Allow treatment of cancer.

Do not allow just “used in medicine”.

OR

57

Co/Co-57/cobalt-57 and medical tests/label for vitamin B12 uptake; 1 max Do not allow just “used in medicine”.

8. A

9. B

10. (a) (let x = fraction of 85Rb)

100

] 87 ) 100 [( ) 85

(x× + −x ×

= 85.47;

85Rb = 76.5 % and 87Rb = 23.5 %; 2

Award [2] for correct final answer.

(b) the (vaporized) ions are deflected by the (external) magnetic field; the 85Rb /lighter ions are deflected more than the 87Rb/heavier ions / OWTTE;

Allow deflection depends on mass to charge ratio or momentum of ions.

the ions are detected by conversion into an electrical current / OWTTE; the ratio of the intensity of the peaks in the spectrum is equal to the ratio of the ions in the sample / the ratio of the height of the

peaks due to 85Rb and 87Rb will be 76.5:23.5 / OWTTE; 3 max

(2)

2 (c) 37 (electrons);

50 (neutrons); 2

11. C

12. A

13. (i) the electron configuration (of argon) / 1s22s22p63s23p6; 1

(ii) x = 1 and y = 5; 1

(iii)

;

4s 3d

Accept all six arrows pointing down rather than up. 1

14. B

15. D

16. (a) average mass of isotopes of an element compared to (1/12 g of) 12C / average mass of an atom relative to C–12 having a mass of exactly 12 / OWTTE;

Allow element instead of atom.

Must refer to average mass and C–12. 1

(b) Diagram of mass spectrometer containing in the correct sequence:

vaporization/vaporized sample; ionization/electron gun;

acceleration/oppositely charged plates; deflection/magnetic field;

detection;

Award [3] for 5 correct labels, [2] for 3–4 correct labels, [1] for 2 correct labels. Award [1] for correct order for at least 4 correct labels.

Award [1] for diagram, which must at least show ionization (e.g. electron beam), acceleration (e.g. charged plates) and deflection (e.g. magnetic

field) even if these are incorrectly labelled. 5

17. 63x + 65(1 – x) = 63.55;

(or some other mathematical expression).

63Cu = 72.5 % and 65Cu = 27.5 %;

Allow 63Cu = 0.725 and 65Cu = 0.275.

Award [2] for correct final answer. 2

18. B

19. B

20. B

21. D

(3)

23.

showing y-axis labelled as energy/E / labelling at least two energy levels; showing a minimum of four energy levels/lines with convergence; showing jumps to n = 1 for ultraviolet series;

showing jumps to n = 2 for visible light series;

Must show at least two vertical lines per series to score third and fourth mark but penalize once only.

For third and fourth marks if transition not shown from higher to lower

energy level penalize only once. 4

24. 1s22s22p63s1;

Do not accept [Ne] 3s1.

first electron easy/easiest to remove / 1 electron in outermost/n = 3 energy level / furthest from nucleus;

large increase between 1st and 2nd IE as electron now removed from n = 2; next 8 electrons more difficult to remove / show (relatively) small increase as these electrons are in the same energy level/second energy level/n = 2; large increase between 9th and 10th IE as electron now removed from n = 1 / 2 electrons very hard/most difficult to remove / innermost/lowest/closest to the nucleus/energy level/n = 1 / OWTTE;

electron 11 also comes from 1s, so shows a small increase; 4 max

25. A

26. C

27. (i) ions/particles accelerated by electric field; ions/particles deflected by magnetic field;

Award [1 max] for acceleration and deflection of ions without

reference to fields. 2

(ii) prevents collisions / avoid false readings due to presence of other particles; 1

28.

100

) 17 . 2 57 ( ) 88 . 91 56 ( ) 95 . 5 54

( × + × + ×

;

55.90;

Award [2] for correct final answer.

Answer must be to 2 d.p. 2

29. (i) energy (per mole) needed to remove one/first/most loosely bound electron from a (neutral) atom;

in the gaseous state; Mg(g) → Mg+(g) + e–;

Gaseous state symbols needed. Accept e instead of e–.

Only penalize omission of gas phase once in either the second marking

point or the third marking point. 3

(4)

4

increased electrostatic attraction; 2

(iii) 10th electron comes from 2nd energy level/n = 2 and 11th electron comes from 1st first energy level/n = 1 / OWTTE;

electron in 1st energy level closer to nucleus;

electron in 1st energy level not shielded by inner electrons /

exposed to greater effective nuclear charge; 3

30. B

31. A

32. (i) a vaporized sample must be used;

bombarded with (high energy) electrons to form positive ions; accelerated by passing through an electric field;

deflected by passing through a magnetic field; detected by producing a current;

Award [2 max] if just the words vaporization, ionization, acceleration,

deflection and detection are used with no explanation. 5

(ii) (size of the positive) charge (on the ion); mass (of the ion);

strength of the magnetic field;

velocity/speed (of the ions) / strength of electric field;

m/z scores the first two marking points. 3 max

(iii) Ar =

100

)] 88 54 . 82 ( ) 87 00 . 7 ( ) 86 90 . 9 ( ) 84 56 . 0

[( × + × + × + ×

;

= 87.71;

Award [1 max] if answer not given to two decimal places. Award [2] for correct final answer.

Apply –1(U) if answer quoted in g or g mol–1. 2

33. C

34. (i) first ionization energy: M(g) → M+ (g) + e–/e / the (minimum) energy (in kJ mol–1) to remove one electron from a gaseous atom / the energy required to remove one mole of electrons from one mole of gaseous atoms;

periodicity: repeating pattern of (physical and chemical) properties; 2

(ii) (evidence for main levels)

highest values for noble gases / lowest values for alkali metals / OWTTE; general increase across a period;

(evidence for sub-levels)

drop in I.E. from Be to B/Mg to Al/Group 2 to Group 3;

drop in I.E. from N to O/P to S/Group 5 to Group 6; 4

(iii) M+(g) → M2+(g) + e–/ OWTTE;

Accept e instead of e–. 1

(iv) Rough sketch to show:

Graph of successive ionization energies for potassium

correct use of axes and one electron relatively easy to remove; a jump in value then eight, another jump to

another eight and finally

another jump for the remaining two electrons;

electronic configuration of K =

1s22s22p63s23p64s1 / first electron due to removal of 4s1, next eight due to third level/3s23p6, next eight due to

(5)

the more electrons removed the more the positive nucleus attracts the remaining electrons and each main energy level is closer to the

nucleus / OWTTE; 4

35. A

36. A

37. D

38. D

39. B

40. D

41. A

42. B

43. C

44. series of lines/lines;

electron transfer/transition between higher energy level to lower energy level / electron transitions into first energy level causes UV series / transition into second energy level causes visible series / transition into third energy level causes

infrared series;

convergence at higher frequency/energy/short wavelength;

Allow any of the above points to be shown on a diagram. 3

45. A

46. A

47. (a) IV < I < II < III/

ultra violet radiation < yellow light < red light < infrared radiation; 1

(b) A continuous spectrum has all colours/wavelengths/frequencies whereas a line spectrum has only (lines of) sharp/discrete/specific colours/

wavelengths/frequencies; 1

(c) UV-B radiation has shorter wavelength; hence, has higher energy;

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