This exam focus covers Worked Model Answer within The Reactivity Series for GCSE Chemistry. Revise The Reactivity Series in Chemical Changes for GCSE Chemistry with 28 exam-style questions and 20 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 11 of 12 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
📝 Worked Model Answer
Question: "Explain why potassium is more reactive than sodium." (6 marks)
Potassium has more electron shells than sodium — potassium has four shells, whereas sodium has three. [1] This means the outer electron in potassium is further from the nucleus than the outer electron in sodium. [1] There are also more inner electron shells in potassium, which provide greater shielding of the outer electron from the attractive force of the positive nucleus. [1] As a result, the electrostatic attraction between the nucleus and the outer electron is weaker in potassium than in sodium. [1] This means potassium loses its outer electron more easily than sodium. [1] Because potassium loses electrons more readily, it is a better reducing agent and reacts more vigorously with water and other substances, making it more reactive overall. [1]
Examiner note: Full marks require ALL four structural points: more shells, greater distance, more shielding, weaker attraction — then the link to easier electron loss and greater reactivity. Partial answers that only say "further from the nucleus" without mentioning shielding typically score 3-4 marks. Many students lose marks by stating the conclusion without explaining the mechanism.
Practice questions for The Reactivity Series
Which of the following shows metals listed in order from MOST reactive to LEAST reactive?
Iron filings are added to copper sulfate solution. Explain what happens, including what is observed and why the reaction occurs.