In Paper 2 this chapter appears as trends down Groups 1, 17 and 18, reactivity comparisons from electron arrangements, displacement reactions, and the special properties of transition elements. This guide shows how to plan an extended answer, gives bullet skeletons, and explains what each command word demands.
Paper 2 (4541/2) is where this chapter is tested at length. It contains Paper 2 has Section A (structured), Section B (limited-response) and Section C (open-response), and The Periodic Table of Elements appears in all three: as short structured parts in Section A and as longer, marks-heavy responses in Sections B and C. This guide shows you how the chapter is set, how to plan a response, and the structure a good answer follows. It does not give you an essay to memorise, the examiner rewards a planned, complete answer in your own words.
How this chapter appears in Sections B and C
Section B is limited-response and Section C is open-response; both give extended tasks built from the chapter’s content standards. The most common forms are:
- Describe and explain a trend down a group, reactivity down Group 1 or Group 17, or boiling point down Group 18, in terms of atomic size and electron arrangement.
- Compare the reactivity of two named elements using their electron arrangements, then justify which is more reactive.
- Describe and explain a displacement reaction between a halogen and a halide salt, with observation and equation.
- Describe the special properties of transition elements, with an example of each property.
- Describe a trend across Period 3, covering atomic size, metallic character and the acid–base nature of the oxides.
- Outline the development of the periodic table, sequencing the contributions from Lavoisier to Moseley.
A planning method that works under time pressure
- Read the command word first and underline it, it tells you what kind of answer earns the marks.
- Break the question into its parts (a), (b), (c) and note how many separate points each part needs.
- Jot a quick skeleton in the margin: for a trend, write “position → structure → prediction” and fill each in.
- Answer in electron-arrangement language. Almost every mark in this chapter is earned by explaining a property in terms of valence electrons, number of shells, atomic size, and how easily an electron is lost or gained.
- Add an equation or a labelled observation wherever the question allows, a word or chemical equation for a reaction, or the colour change in a displacement.
- Check every part is answered before moving on; unanswered parts are the biggest avoidable loss.
Model-answer skeleton: “Explain the trend in reactivity down Group 1”
Use this as a structure, not a script. Fill it with the named elements.
- State the trend: reactivity increases down Group 1.
- Give the structure: each atom has one valence electron; going down the group, the number of shells increases and the atom becomes larger.
- Link size to the electron: the valence electron is further from the nucleus and is held less tightly (the attraction from the nucleus is weaker).
- Give the prediction: the electron is therefore lost more easily, and losing that electron is what the reaction requires, so the lower element is more reactive.
- Support with an example: potassium reacts more vigorously with water than sodium does.
Model-answer skeleton: “Explain why reactivity decreases down Group 17”
- State the trend: reactivity decreases down Group 17.
- Give the structure: each atom has seven valence electrons; going down, the atom becomes larger with more shells.
- Link size to the electron: the nucleus attracts an incoming electron less strongly because it is further away and shielded.
- Give the prediction: the atom gains an electron less easily, so the lower halogen is less reactive.
- Support with an example: chlorine displaces bromine from a bromide, showing chlorine is the more reactive.
Notice that the two skeletons are mirror images: Group 1 is about losing an electron, Group 17 about gaining one. Stating which process the group depends on is the pivot of the whole answer.
Model-answer skeleton: “Describe the special properties of transition elements”
- form coloured ions and compounds (example: copper(II) compounds are blue);
- show variable oxidation numbers (example: iron as Fe²⁺ and Fe³⁺);
- act as catalysts (example: iron in the Haber process);
- form complex ions; and are hard, strong metals with high melting points and densities.
Give a named example for each property, an unsupported list scores less than a list where every property is illustrated.
Model-answer skeleton: “Describe and explain the trend across Period 3”
- Atomic size: decreases from sodium to chlorine, because the proton number increases while electrons stay in the same shell, so the greater nuclear charge pulls the shells inward.
- Metallic character: decreases, the metals sodium, magnesium and aluminium give way to the metalloid silicon and then the non-metals phosphorus, sulfur and chlorine.
- Oxides: change from basic (sodium and magnesium oxide) through amphoteric (aluminium oxide) to acidic (oxides of phosphorus and sulfur).
- Tie it together: the shift from metal to non-metal and from basic to acidic oxide both follow from the increasing number of valence electrons across the period.
Command words, what each one demands
- State / name, give a short, exact answer with no explanation (for example, “Group 17” or “hydrogen”). Do not waste time explaining.
- Describe, say what happens or what the trend is, in order, without necessarily giving the reason (for example, describe how colour changes down Group 17).
- Explain, give the reason, in electron-arrangement terms. This is where most marks in this chapter sit; a description alone will not score an “explain” mark.
- Compare, give the points of difference (and similarity) for both elements, using comparative words such as “more”, “less”, “larger”, never describe only one.
- Predict, state the expected property from the element’s position, then justify it with the structure.
A worked plan
Suppose a question reads: “Sodium and potassium are Group 1 metals. Compare and explain their reactivity with water.” The command words are compare and explain, so the answer must cover both elements and give reasons, not just a description. Skeleton in the margin: (1) both have one valence electron; (2) potassium is lower, more shells, larger atom; (3) potassium’s valence electron is further out and held more loosely; (4) so potassium loses its electron more easily and is more reactive; (5) example, potassium reacts more vigorously, and may ignite. With those five points laid out, you write a full paragraph that earns every mark without rushing. Points (3) and (4) are the “explain”; the word “more” on each point satisfies “compare”.
Turning the plan into marks
Every high-scoring answer in this chapter runs the same line: name the position, describe the structure (valence electrons and shells), then explain the property or trend, and support it with an equation or example. Keep your reasons in electron-arrangement language and answer every part. A one-to-one teacher can mark a full Section B or C response against this structure and show you exactly where a reason or a comparison is missing, the difference between a partial and a full-mark answer in the SPM Chemistry Paper 2.
Want a teacher to make this click?
We teach SPM Chemistry one to one, so your child understands it and scores it.
from RM50/hr · One-hour paid trial · Same-day reply