A-LevelChemistryAtomic structure9701/21 · May/June 2025 · Q211 Marks

A sample of iron is analysed using a mass spectrometer. The mass spectrum shows three isotopes of iron are present in the sample.

(a)Define isotopes.[1]
(b)(i)Use Fig. 2.1 to calculate the relative atomic mass, Ar, of iron to one decimal place. Show your working. [Figure 2.1][2]
(b)(ii)Complete Table 2.1 to show the number of protons and nucleons in one atom of 56Fe. Table 2.1 particle number of particles in one atom of 56Fe protons nucleons [2]
(c)Deduce the number of pairs of electrons in the shell with principal quantum number n = 3 in an Fe atom.[1]
(d)Write an equation to represent the first ionisation energy of iron.[1]
(e)Suggest how the value for the first ionisation energy of 54Fe compares to the first ionisation energy of 56Fe. Explain your answer in terms of the factors that affect ionisation energy.[4]

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Mark scheme

Marking points from the official mark scheme (May/June 2025). The mark or mark type is shown in brackets.

[1] atoms (of an element) with same number of protons and different number of neutrons
[2] M1 method showing each abundance multiplied by m/e value • (5.9 × 54) and (91.9 × 56) and (2.2 × 57) OR • (0.59 × 54) and (9.19 × 56) and (0.22 × 57) M2 the three values from M1 expressed as a percentage and added together correctly with final answer to 1 d.p 5.9 / 100 × 54 + 91.9 / 100 × 56 + 2.2 / 100 × 57 = 55.9
[2] protons: 26; nucleons: 56
[1] 5
[1] Fe(g) → Fe+(g) + e(-)
[4] M1 same electronic configuration OR same shielding; M2 same number of protons OR same nuclear charge; M3 so same nuclear attraction to outer shell electron; M4 no change / will not be affected

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