A-LevelChemistryChemical energetics9701/42 · May/June 2022 · Q39 Marks

Define first electron affinity.

(a)(i)Define first electron affinity.[2]
(a)(ii)The first electron affinity of an atom is usually an exothermic process, whereas the second electron affinity is an endothermic process. Suggest why.[1]
(a)(iii)Describe the general trend in first electron affinities for Cl, Br and I. Explain your answer.[2]
(b)Table 3.1 shows energy changes to be used in this question and in (c). [Figure Table 3.1] Calculate the first electron affinity for iodine. Use relevant data from Table 3.1 in your working. It may be helpful to draw a labelled energy cycle. Show all working.[3]
(c)Predict how ∆Hatt of CdI₂(s) differs from Hatt of ZnI2(s). Place a tick (✔) in the appropriate box in Table 3.2. [Figure Table 3.2] Explain your answer.[1]

Mark scheme

Marking points from the official mark scheme (May/June 2022). The mark or mark type is shown in brackets.

[2] enthalpy change / energy change
[2] one mole of electrons
[2] (gained by) one mole of gaseous atoms
[1] (energy required to overcome) the repulsion between the electron and anion / negative ion
[2] less negative / less exothermic down the group
[2] greater the distance between the nucleus and (the shells of the) electrons OR atomic radii increases OR more shielding by inner shells
[2] the less attraction between nucleus and incoming electron (and the less energy released)
[3] M1 use of correct seven numbers only in calculation / energy cycle
[3] M2 only 2 x used correctly
[3] M3 correct signs and evaluation ecf
[1] first box ticked
[1] AND Cd2+ larger / Cd2+ lower charge density
[1] AND less attraction between the ions / weaker ionic bonds

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