CAIE A Level Chemistry 9701 · The Periodic Table: chemical periodicity
Consider the oxides of the elements sodium to sulfur in Period 3: , , , , and , and the chlorides , , , and .
Explain why the oxidation number of the element in the oxide and in the chloride increases across the period, using the outer shell electrons of the elements.
4 marks, so the mark scheme is looking for about 4 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.
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