IB Chemistry HL 3.1.9 Variable Oxidation States Question Bank

Explain variable transition-metal oxidation states using accessible d and s electrons.

Exam points

use electron structure and periodic position to justify a trend
compare relevant atoms, ions or compounds with correct terminology
link observations to effective nuclear charge, shielding or d electrons

[Maximum number: 3]

Beryllium is a low-density metal that is used in specialized lightweight alloys.

Iron (III) chloride also exists as a dimer in the vapour phase, but iron, unlike beryllium, is a transition element.

The first four ionization energies of beryllium and iron are shown.

Figure for Question 3.1.9 (HL)—Variable oxidation states question 1 — IB Chemistry HL

One common property of transition elements is that they have variable oxidation states. Discuss, referring to the graph, why iron, but not beryllium, displays this characteristic.

IE values of Fe gradually increase

AND

IE values of Be show a sudden rise

first and second ionization energies close together therefore do not form a +1 oxidation state / singly charged ion

further IEs of Fe are close to second IE, so the oxidation state/number of electrons Fe loses can vary «according to the oxidizing agents present»

Marking guidance:

Accept Be always loses 2 electrons /
forms $\mathrm{Be}^{2+}$ / only has +2 oxidation state
for M2 .

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3.1.9 (HL)—Variable oxidation states question 1