Q23 · 2022 · Paper 1Complex familiar6 marks
QUESTION 23 (6 marks)
The diagram shows the electron energy levels for hydrogen.
a)[3 marks]
Calculate the energy released, in joules, when an electron moves from the third to the first energy level. Show your working.
b)[3 marks]
Explain why hydrogen only has four emission spectrum lines in the visible (i.e. 400–700 nm) spectrum.
WORKED SOLUTION
6 marksQCAA guide · typeset solution
ANSWER
See worked solution below.
Worked solution
(
)
1
12.09
1 9
18
18
10
0
13.60
.
1.51
. 3
1 93
E
eV
J or
J released
E
E
i
f
∆
= −
−
−
−
−
=
−
×
−
−
=
×
=
Energy released = 1.93 × 10−18 J (to three significant
figures)
Emission spectrum lines relate to the wavelength of light
produced by the release of energy as an electron moves
from a higher energy level to a lower energy level within an
atom. Since light in the visible spectrum corresponds to
wavelengths between 400–700 nm, only energy emitted
with wavelengths within this range will be observed. This
corresponds to electrons moving between levels where
n = 2, 3 or 4.
• recognises the scenario relates to the change in
electron energy as it moves between energy
levels [1 mark]
• determines the energy released [1 mark]
• converts energy from electronvolts to joules
[1 mark]
• explains the relationship between emission lines
and orbital energies [1 mark]
• identifies that only transitions occurring between
orbitals where the energy difference corresponds
to wavelengths between 400–700 nm would emit
visible light [1 mark]
• identifies specific aspects of the energy level
diagram to support the explanation [1 mark]
One QCAA sample method typeset for web; criterion wording is adapted from the official marking guide.
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Compare your working with the guide above.