The kind of SPM questions asked on the periodic table

The Periodic Table of Elements is one of the most structured chapters in Form 4: almost every question follows from one idea, that an element’s electron arrangement fixes its position and its position predicts its behaviour. Once you can move confidently between arrangement, group, period and trend, the chapter’s question types become easy to recognise. Here they are, sorted, with the move that scores each.

Type 1: Position from electron arrangement

The foundational type gives an electron arrangement and asks for the group and period, or vice versa. The two rules are: the group number equals the number of valence electrons (for Groups 1, 2 and 13–18), and the period number equals the number of occupied shells.

Worked example: An atom has the electron arrangement 2.8.1. It has one valence electron, so it is in Group 1; it has three shells, so it is in Period 3. That element is sodium. Getting both numbers, and not just one, is what earns full marks here.

Type 2: Group 18, the noble gases

A short but frequent type asks why the noble gases are unreactive. The answer is their stable electron arrangement, a duplet for helium and an octet for the rest, so they have no tendency to gain, lose or share electrons.

Worked example: Explain why argon does not form compounds easily. Argon has the arrangement 2.8.8, a full outer shell, so it is chemically stable and inert. Noble gases are also used as the benchmark against which other atoms “want” to react, to reach a noble-gas arrangement.

Type 3: Group 1, the alkali metals

A high-frequency type asks about the trend in reactivity down Group 1 and the reaction with water. Down the group, reactivity increases: the atom gets larger, the single valence electron is further from the nucleus and more easily lost, so the metal reacts more vigorously.

Worked example: Compare the reaction of lithium and potassium with water. Both give a metal hydroxide and hydrogen gas, for sodium, 2Na + 2H₂O → 2NaOH + H₂. Potassium, lower in the group, reacts far more vigorously than lithium. The full reaction is on our Group 1 metals with water page.

Type 4: Group 17, the halogens

The mirror-image type asks about Group 17, where reactivity decreases down the group: the atom gets larger, so it attracts an incoming electron less strongly and reacts less readily. Two reactions recur, with iron and by displacement.

Worked example: Chlorine displaces bromine from potassium bromide because chlorine is more reactive (higher in the group): Cl₂ + 2KBr → 2KCl + Br₂, and the colourless solution turns brown as bromine forms. A more reactive halogen always displaces a less reactive one; practise more on our displacement of halogens page.

Type 5: Change across a period

A trend type asks how properties change across Period 3, from sodium to argon. Across the period the elements change from metallic to non-metallic, the atomic radius decreases (the growing nuclear charge pulls the same shell in tighter), and the oxides change from basic to acidic.

Worked example: State how the metallic character changes from sodium to chlorine across Period 3. It decreases, the elements go from reactive metals on the left, through the metalloid silicon, to reactive non-metals on the right. Being precise about the direction of the trend is the whole mark.

Type 6: Transition elements

Finally, a description type asks for the special properties of the transition elements: they show variable oxidation states, form coloured compounds and ions, and act as catalysts (iron in the Haber process, for example). Listing these correctly, with an example each, is a reliable source of marks in a longer answer.

Revising across the six

Because the same six types return, revise by move: convert an arrangement into a position, explain noble-gas stability, state the Group 1 and Group 17 trends with a reaction each, describe the across-period change, and list the transition-metal properties. That is how our online one-to-one lessons work through this chapter, in English from RM50 an hour with a paid one-hour trial. Anchor every answer to electron arrangement, and the Periodic Table becomes one of the most predictable, and rewarding, chapters in the paper.