State the full electronic configuration of Fe²⁺.

Explain why there is a large increase from the 8th to the 9th ionization energy of iron.

Calculate the oxidation state of sulfur in iron(II) disulfide, FeS₂.

Describe the bonding in iron, Fe (s).

1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ ✔

Any two of:

IE₉: electron in lower energy level
OR
IE₉: more stable/full electron level ✔

IE₉: electron closer to nucleus
OR
IE₉: electron more tightly held by nucleus ✔

IE₉: less shielding by «complete» inner levels ✔

–1 ✔

Accept “– I”.

electrostatic attraction/hold between «lattice of» positive ions/cations AND delocalized «valence» electrons ✔

Mostly well done which was a pleasant surprise since this is not overly easy, predictably some gave [Ar] 4s² 3d⁴.

Despite some confusion regarding which sub-level the electrons were being removed from, many candidates were able to make at least one valid point, commonly in terms of lower energy/ full sub level/closer to nucleus.

This was an easy question, yet 30% of the candidates were unable to work it out; some wrote the oxidation state in the conventionally incorrect format, 1- and lost the mark.

Most candidates knew the bonding in Fe is metallic but some did not “describe” it or missed the type of attraction, a minor mistake; others referred to nuclei or protons instead of cations/positive ions. In some cases, candidates referred too ionic bonding, probably still thinking of FeS₂ (not reading the question well). Overall, only 30% answered satisfactorily.