Aim for FiveChemistry

Short free-response question

Reading a photoelectron spectrum

  • Unit 1
  • 4 points
  • About 9 minutes

You can use a calculator on this question, just like on exam day.

A shorter multipart question that sticks to one or two topics. Each part usually asks for one calculation, claim or explanation. On the exam: 4 questions (Questions 4–7), part of the 1-hour-45-minute free-response section; calculator allowed.

The question and its sources

The photoelectron spectrum (PES) of a gaseous sample of an element has four peaks. The table gives the binding energy of each peak and its relative height (proportional to the number of electrons).

Table 1. PES peaks of an unknown element

PeakBinding energy (MJ/mol)Relative number of electrons
A1042
B6.842
C3.676
D0.501

Source: Standard values, rounded

Suggested time: 9 minutes

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Part (a)

1 point

Identify the element, and write its complete ground-state electron configuration.

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Part (b)

1 point

The binding energy of peak A is much greater than the binding energy of peak D. Explain this difference using Coulomb's law.

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Part (c)

1 point

Describe how the peak for the 3s electrons in the PES of magnesium would compare with peak D, in terms of both its binding energy and its relative height. Justify your answer about binding energy.

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Part (d)

1 point

Describe how the PES of the Na⁺ ion would differ from the spectrum in Table 1.

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