CAIE A Level Chemistry 9701 · The Periodic Table: chemical periodicity
A student reacts samples of the Period 3 elements sodium, magnesium, aluminium, silicon, phosphorus and sulfur with oxygen. In separate experiments, the student also reacts sodium, magnesium and aluminium with chlorine. Explain the variation in the oxidation number of the oxides formed, and the variation in the oxidation number of the chlorides formed, in terms of the outer shell (valence shell) electrons of the elements.
7 marks, so the mark scheme is looking for about 7 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.