Bohr’s Atomic Model & Line Spectrum

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Past Year Examination Questions Unit 2

14

Unit 2: Atomic Structure

Bohr’s Atomic Model & Line Spectrum

Jan 99

1. What conclusion did Bohr draw in his atomic model to explain the line spectrum of hydrogen?

2. The Brackett series of the spectral line of atomic hydrogen appears in the infrared region. The

wavelength for the third line in Brackett series is 2166 nm.

i. Why the hydrogen atomic spectrum is in the form of lines?

ii. Explain how the third line of the Brackett series is formed.

iii. Calculate the energy involved to form the third line in the Brackett series. <9.18X1020>

Jun 99

3. The frequencies for the five lines in the Balmer series of the atomic hydrogen line emission

spectrum are as follows:

4.57, 6.17, 7.31, 7.55 and 7.71 ( x 1014 Hz)

i. Copy the following diagram of energy levels and draw arrows to show the transitions of

electron of hydrogen atom which correspond to the given frequency values.

ii. Calculate the wavelength of the third line in the Balmer Series. <434nm>

n=1

n=2

n=3

n=4

n=5

n=6

n=7 n=8

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Jun 00

4. State two main postulates from Bohr’s Atomic Theory and explain its main inadequacies.

State the de Broglie’s postulate and Heisenberg Uncertainty Principle, and give their

corresponding equations.

5. Explain the differences between Lyman series and Balmer series in an emission spectrum.

Jan 00

6. Calculate the energy required to promote an electron from the first orbit to the third orbit of a

hydrogen atom. <1.94X10-18>

7 What is meant by ionisation energy of hydrogen? Explain briefly how the ionisation energy of

hydrogen can be obtained from the spectral line of atomic hydrogen. Calculate the ionisation

energy of hydrogen in kJ mol1. <1312>

UPS 01

8. An electron of a hydrogen atom is excited to the energy level n=5 and drops to a lower level

energy forming Paschen series.

i. State the energy level whereby the electron ‘dropped back’. <n=3>

ii. Calculate the energy of the electron at the excited level. <8.72x1020>

iii. Calculate the energy emitted as a result of the transition. <1.55x1019>

9. Copy the following energy levels diagram and show the transitions of electrons that account for

the formation of the first, second and third line in the emission spectrum of hydrogen atom.

Energy

a) Calculate the energy involved when the electron transits from the fourth orbit in order to

form Balmer series. <4.09x1019>

b) State whether the energy is absorbed or released for this particular transition. Explain.

Aug 01

10. Calculate the wavelength of the third line in the Lyman series of hydrogen spectrum. <97.2 nm>

Determine the ionisation energy for 1 mole of hydrogen. <1312>

n=1

n=2

n=3

n=4

n=5

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Aug 02

11. One of the lines in the atomic hydrogen line emission spectrum falls in the visible light region

and has a wavelength of 410.2 nm.

i. Explain the meaning of line spectrum.

ii. Give the name for this spectrum series.

iii. Determine the transition of the electron involved.

MST Jun 02

12. One of the lines in the Balmer series of the atomic hydrogen emission spectrum has a

wavelength of 486.2 nm.

From which energy level does it drop from to give rise to this particular line?

MST Jun 03

13. a) State de Broglie’s postulates and Heisenberg Uncertainty principle.

b) When a hydrogen atom absorbs energy, its electron is promoted to the 5th orbit. A line

spectral is formed in the visible region resulting from the transition of the electron to a

lower energy orbit.

Calculate the wavelength and energy of the emitted photon.

Sept 03

14. Explain the formation of line spectrum in the Balmer series of hydrogen atom.

If the emitted photon has a wavelength of 434 nm, determine the transition of the electron that

occurs.

Calculate the energy of the line with the lowest energy in the Balmer series in kJ mol1. <1.82x102>

MST Jul 04

15. a) Describe a continuous spectrum and explain how it differs from an atomic spectrum.

b) Briefly describe what would occur when an electron in a hydrogen atom falls from an

orbital to another with a lower energy.

c) If the electron of a hydrogen atom had initially been in its 6th Bohr’s orbit, determine the

frequency of the electromagnetic radiation emitted if it forms a line spectral in the

Paschen series.

Oct 04

16. Explain why an atomic emission spectrum consists of series of lines.

MST Jul 05

17. An electron of a hydrogen atom is excited to an energy level of n=7 and falls to a lower energy

level to produce Paschen series.

i. State the energy level to which the electron falls.

ii. Calculate the energy of the electron in the excited state.

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Oct 05

18. Figure below shows the line spectrum of hydrogen atom in the visible region.

i. Draw the energy levels in a hydrogen atom.

ii. Show the electron transitions which produce the above lines.

iii. Give the name of this particular series of lines.

MST July 06

19. i. Calculate the wavelength and frequency of the light that forms the third line of the Brackett

series.

ii. Calculate the energy of an electron at its excited state before it drops to produce the second

line of the Balmer series.

MST July 07

20. (a) Give the difference between a line spectrum and a continuous spectrum.

(b) An electron of a hydrogen atom is excited to the energy level n = 4 and drops to a lower

energy level to form a line in the Balmer series.

i. Calculate the energy of the electron at the energy level n = 4.

ii. Determine the wavelength of this transition.

Oct 07

21. State the success and failure of Bohr`s atomic model.

Calculate the wavelength for a spectral line produced when an electron falls from n = 5 to n = 3.

Name the series and state the region of electromagnetic spectrum for the line.

Quantum Mechanics Model

Jan 99

22. a. With suitable examples, explain the meaning of the Pauli exclusion principle, Hund’s

rule and Aufbau principle.

b. What is the meaning of orbital?

c. Write the electronic configuration for 24Cr. Sketch the shape of the electron occupied

orbital in the outmost shell and describe its set of quantum numbers.

Jun 99

23. Draw the shapes of py and dxy orbitals. Show the symmetry and the coordinate axes in each

orbital diagram.

State the quantum numbers for the 3dxy orbital.

red blue indigo violet

Frequency

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24. Orbitals of an atom can be recognised through a set of four quantum numbers which

characterise the orbitals.

i. Name the four quantum numbers mentioned above and state the characters determined by

each quantum number.

ii. Write the electronic configuration for 38Sr and give the corresponding values of all the

four quantum numbers for the electrons in the valence shell.

Jan 00

25. Explain why the following sets of quantum numbers are unacceptable in an atom.

n = 2, l = 1, m = 1, s = 1

n = 3, l = 1, m = 2, s = +1/2 (2M)

26. Given the following sets of quantum numbers for three electrons at the highest energy orbitals

for an atom J.

(3, 2, 0, -21 ) , (3, 2, +1,

21 ) , (3, 2, 1,

21 )

Describe the types of orbitals designated by the above sets of quantum numbers.

Name the quantum number that determines the shape of the orbital.

Give the electronic configuration and the orbital diagram for atom J. Hence, determine its

valence shell.

If five electrons were taken away from atom J, write the electronic configuration and the orbital

diagram for the ion formed.

State the type of stability for the electronic configuration of this ion.

Jun 00

27. For a multiple-electron atom, arrange the following orbitals in order of increasing energy:

6p , 4d , 4s , 4f , 3p , 3d , 5s (1M)

28. Write the electronic configuration in the ground state for Al and Ti+.

MST 01

29. The table below shows the elements P, Q and R with their respective proton numbers.

Element Proton number

P 16

Q 25

R 28

i. Give the electronic configuration and draw the orbital diagram for elements P and Q.

ii. What is meant by orbital?

iii. Draw the shapes of the orbitals that accommodate the valence electrons for elements P

and Q.

iv. Compare the size of the atom P, Q and R. Explain.

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30. The table shows the proton numbers for five elements S, T, U, V and W.

Element Proton number

S 7

T 8

U 9

V 11

W 13

i. State the group and period for element U and W.

ii. Pick a block-p element.

iii. Predict the oxidation number for T and W.

iv. Arrange the elements S, T, U, V and W in order of increasing atomic radius. Explain.

Mac 01

31. Give the values of and m for orbitals 3p and 4d.

Mac 02

32. An element N has proton number 22. Explain how Hund’s rule, Pauli exclusion principle and

Aufbau principle are used in the placement of electrons into the orbitals for N.

Draw the orbital diagrams for the four outermost electrons in element N. Hence, give the

quantum number set for all these four electrons.

MST Jul 03

33. a) Write the electronic configuration for element 27X.

b) State the four quantum numbers of the last electron being filled to the orbital according

to Aufbau principle.

MST Jul 04

34. On appropriate coordinate axes, sketch out any two orbitals of an electron characterised by the

principal quantum number of 3 and the azimuthal quantum number of 2.

35. (a) Define an orbital. Sketch the shape of the orbital dxy2-y2 and dxy

(b) State the electron configuration and orbital notation for chromium. What is the principle

used in the arrangement of electron in an orbital. (Ar Cr : 24)

(c) Calculate the wavelength and the energy of the third line in the Brackett series of the

hydrogen spectrum.

(d) State a value for n, l and m1 of an orbital in 4d sub-shell.

Oct 04

36. Copper is the ninth element in the first row of d-block of the Periodic Table.

i. Write the electronic configuration of copper according to the Aufbau principle and the

actual configuration as determined by experiments.

ii. Give reason(s) for any anomaly.

iii. Name another transition element which shows similar anomaly and write the electronic

configuration showing the anomaly.

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MST Jul 05

37. i. Define the terms orbit and orbital.

ii. Chromium is an element in d-block of the periodic table. Write the electronic

configuration of chromium. Explain the anomalous electronic configuration in chromium.

iii. Give a set of quantum numbers for an electron in 3p-orbital.

Oct 05

38. State Aufbau principle and Hund’s rule. Based on the principle and rule above, show how the

electronic configuration of element 26G is built.

Draw the dxy

and dx2y2 orbitals in 26G and the possible azimuthal and magnetic quantum

numbers for each of the orbital.

MST Jul 06

39. i. State the quantum number n , ℓ and m of the 3d x2

- y2 orbital and draw its shape.

ii. Write the electronic configuration of Mn and Mn2+ .

Oct 06

40. Write the electron configuration of iron(II) and iron(III). Determine the values of n , ℓ , m and s

for the electrons in the outermost shell in iron(III).

Compare the size of these two ions.

MST Jul 07

41. The orbitals of the first two principal energy levels of atoms are shown below.

In an atom of element J, orbitals A, B and E are full of electrons while orbitals C and D are half

full.

i. State the charge of J ion. Briefly explain your answer.

ii. Write the electronic configuration of J.

iii. State the quantum number n, l and m for orbital D.

XY

Z

A

XY

Z

C

X

Y

Z

D

X

Y

Z

B

X

Y

Z

E

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Oct 07

42. Name the two transition elements that show anomaly in their electronic configurations.

Write the electronic configuration and explain your answer.

Oct 08

43. i. A hydrogen atom requires a minimum energy of 2.18 x 10 – 18 J atom – 1 to remove an electron

from its ground state level. Determine whether a blue-violet light with a wavelength of 434.0

nm can affect this process.

ii. The excited electrons of a group of irradiated hydrogen atoms are randomly scattered to n= 1,

2, 3, and 4 energy levels. Draw an energy level diagram to show all possible lines produced

when all these electrons drop to lower levels. Identify the line which has the shortest

wavelength.

44. The proton number of elements J and K are 13 and 16 respectively. Draw the orbital diagram

for the valence electrons of each element. Suggest the most stable ions for J and K. write their

respective electronic configurations.

MST Jul 09

45. a) FIGURE 2 shows the Lyman series of hydrogen emission spectrum.

P Q R

FIGURE 2

i) Draw the electronic transition of lines P, Q and R on the energy level diagram of the

hydrogen atom.

ii) Calculate the energy corresponding to line Q.

b) The proton number of element T is 20.

i) Write the electronic configuration of element T.

ii) Predict the stable oxidation number of element T. Explain.

iii) Draw the shape of orbital and give a set of quantum numbers for the valence electron.

Oct 09

46. Find the number of electrons in a zinc atom with

i) orbital quantum number, l, equals to 1

ii) magnetic quantum number, m, equals to -1

iii) l = 3 and m = +1

iv) s = -1/2

47. Write an electronic configuration for argon and give two oppositely charged ions having the same

electronic configuration as argon.

State how a line spectrum differs from a continuous spectrum. Draw four lines in the visible

region of the line spectrum of hydrogen and indicate the low and high energy ends.

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MST 2010/2011

48. (a) FIGURE 2 shows the Lyman series of hydrogen emission spectrum.

P Q R

FIGURE 2

(i) Explain why each successive line becomes closer to the previous one until the lines

form a continuous.

(ii) Calculate the frequency of the light that produce line Q [6 marks]

(b) Element M has 15 protons.

(i) Write the electronic configuration of M3-

(ii) Give a set of quantum numbers for an electron in the 3s orbital

(iii) State two differences between 2s and 3s orbitals [ 4 marks]

2010/2011

49. A line with a wavelength of 486.4 nm was observed in the Balmer series of the emission

spectrum of hydrogen.

(i) Calculate its frequency

(ii) Determine the initial and final values of the energy levels associated with this

emission.

(iii) State the region of the electromagnetic spectrum in which the line is found.

[5 marks]

50. State and explain the appropriate rules used to determine the arrangement of

electrons in atomic orbitals.

The proton number of copper is 29. Write the valence electronic configuration of the copper

atom. Give a set of quantum numbers for the valence electron that occupy the s orbital of

copper. [8 marks]

MST 2011/2012

51. (a) FIGURE 2 shows the Balmer series of hydrogen emission spectrum.

A B C D E

FIGURE 2 (i) State the electron transition that produces line B.

(ii) Explain the formation of line B.

(iii) Calculate the energy of photon that produces line C with the

Wavelength of 434 nm.

[6 marks]

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(b) The following sets of quantum numbers represent the 3 outermost electrons of

element Y at ground state.

n = 3 ℓ = 0 m= 0 s = +1/2

n = 3 ℓ = 0 m = 0 s = -1/2

n = 3 ℓ =1 m=0 s = +1/2

(i) What is the maximum number of orbitals that exits in the shell n=3?

(ii) Write the electronic configuration of element Y.

(iii) Draw the shapes of orbitals for the valence electrons.

[4 marks]

2011/2012

52. (a) FIGURE 1 shows the Lyman series of the hydrogen line spectrum.

10.97 10.66 10.52 10.27 9.74 8.22

wave number (μm-1)

FIGURE 1

Describe the formation of the line emission spectrum of hydrogen atom in the

Lyman series. Calculate the ionization energy (kJmol-1) of the hydrogen atom

using FIGURE 1. Name two species that exhibit similar line spectrum as that

of hydrogen atom.

[10 marks]

(b) For each of the following elements:

Sodium, Magnesium, Alumunium and Silicon

Give the formula, the type of bonding present and the acid base character of

its oxides. For those oxide(s) that exhibit amphoteric behaviour, write an

appropriate chemical equation to illustrate the properties.

[10 marks]

2012/2013

53. (a) Describe the formation of emission spectrum for hydrogen atom. Show

and label the first three series of electron transitions between energy

levels.

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An electron in a hydrogen atom is transferred from n = 5 to n = 3.

Calculate the energy of the photon emitted and the wavelength of the

spectral line produced.

[8 marks]

(b) An element Q has proton number of 8. Draw the orbital diagram of the

element. Explain the two rules applied in arranging the electrons in the

orbitals.

[5 marks]

MST 2012/2013

54. (a) FIGURE 1 shows the first four lines in the Brackett series of hydrogen

emission spectrum.

(i) State the region of the electromagnetic spectrum in which the series is

found.

(ii) Which line corresponds to the shortest wavelength? Calculate the

wavelength of the radiation that produces the line.

[5 marks]

(b) E is an element with proton number of 21.

(i) Write the electronic configuration of E.

(ii) Draw the shapes of orbitals occupied by the valence electrons.

(iii) Give the sets of quantum numbers for the electrons that occupy the

fourth shell.

[5 marks]

MST 2013/2014

55. (a) In the hydrogen atom, an electron transition from a higher to a lower energy

level emits a photon with a wavelength of 1282 nm in Paschen series.

(i) Determine the energy level of the exited state for this transition.

(ii) State the radiation region for this transition.

[5 marks]

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(b) Give the set of quantum numbers for the highest energy electron in atom X:

(4, 1, 0, +1/2)

(i) Write the electronic configuration of X.

(ii) What is the most stable ion of X? Write its electronic configuration.

(iii) Draw the shapes of orbitals occupied by the electrons with the highest

principle quantum number in X.

[5 marks]

2013/2014

56. Bohr used the information from a line spectrum of a hydrogen atom to

explain the electronic structure of a one-electron system. A blue line in the

spectrum of hydrogen atom was observed as a result of a transition of

electron from the fourth to the second shells of an atom. What is meant by

a line spectrum?. Calculate the wavelength and energy for this blue line.

State two of Bohr’s postulates. [8 marks]

MST 2014/2015

57. (a) Calculate the ionisation energy of hydrogen atom in KJ mol-1

[4 mark]

(b) (i) State Heisenberg’s uncertainty principle.

(ii) Give one Bohr’s postulate that is contradictory to the above principle.

[2 mark]

(c) Two orbital diagrams for the electronic configurations shown below are not

allowed. State the principle that are not obeyed and explain.

(i) 2s 2p

(ii)

[4 marks] 2014/2015

58. The ion of atom X has 8 outermost electrons and 10 inner electrons with a charge of -

1. Discuss all the rule(s) and principle(s) used to fill the electrons in the orbital of

atom X. Explain the change in the radius of atom X as it changes from a neutral atom

to be negatively charged ion.

Atom X, Y and Z are in periods n, n + 1 and n +2, respectively. These atoms are also

in the same group. Discuss the trend in electronegativity exhibited by these atoms.

[20 marks]

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MST 2015/2016

59. (a) An electron of a hydrogen atom undergoes a transition to produce a line in the

Pachen series with a wavelength of 1094 nm.

(i) State the region of the electromagnetic spectrum for the above wavelength.

(ii) Determine the energy level of the excited state for this transition. State the

transition involved to form the emission.

[ 4 marks]

(b) (i) Define orbital.

(ii) Write the electronic configuration of the valence electrons for arsenic,

As (iii) Give a set of quantum numbers of one valence electron in the s orbital in

(b)(ii)

[ 4 marks]

(c) Draw and label one of the three-dimensional shapes of d orbitals where

electron occupied the space that lie on the axes. [ 2 marks]

2015/2016

60. Calculate the first three wavelenghts of the possible transitions of an electron in the

Paschen series for a hydrogen atom. Show these wavelengths in a sketch of the line

spectrum for this emission series. Explain how these transitions occurred.

[10 marks]

2016/2017

61. State the difference between the ground state and excited state of an electron in an

atom.

An electron of a hydrogen atom is excited to n = 6 and falls to a lower energy level

forming the Paschen series. Calculate in kJ mol-1, the energy of the electron at the

excited level and the energy emitted as the result of the transition.

Determine the shortest wavelength in nanometers (nm) in the Paschen series for the

hydrogen atom.

[10 marks]

2017/2018

62. Sketch the energy level diagram to show the electronic transitions which give rise to the first

five lines in the Lyman series of the hydrogen atom. Explain how a hydrogen line spectrum is

obtained. Draw the resulting line spectrum.

[10 marks]

Documents

Bohr’s Atomic Model & Line Spectrum