Q26 · 2021 · Paper 1Complex familiar5 marks
QUESTION 26 (5 marks)
A physicist has identified the absorption spectrum of an unknown atom.
The diagram shows the atomic energy levels for three atoms.
Determine which atom is most likely to be the unknown atom.
WORKED SOLUTION
5 marksQCAA guide · typeset solution
ANSWER
See worked solution below.
Worked solution
Each wavelength of light corresponds to a quantum of
energy, which can be worked out using the following
equation:
𝐸= ℎ𝑓= ℎ𝑐
𝜆
The energies that have produced the three wavelengths of
light are:
Line 1: 421 nm
E = 4.72 x 10–19 J = 2.95 eV
Line 2: 491 nm
E = 4.05 x 10–19 J = 2.53 eV
Line 3: 523 nm
E = 3.8 x 10–19 J = 2.38 eV
Compared to the energy level diagrams, only Atom 2 has
three electron transitions that match the wavelengths given:
5 to 2, 4 to 2 and 3 to 2.
• recognises how absorption spectra relate to
energy level diagrams [1 mark]
• determines the energy of photons absorbed by
the atom [1 mark]
• converts from joules to eV [1 mark]
• identifies energy level transitions corresponding
to absorbed photons [1 mark]
• determines the atom [1 mark]
One QCAA sample method typeset for web; criterion wording is adapted from the official marking guide.
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