Edexcel GCSE Chemistry Topic 6: Groups in the Periodic Table Exam Questions

About Edexcel GCSE Chemistry Topic 6: Groups in the Periodic Table

Topic 6 of Edexcel GCSE Chemistry studies three groups in detail: the alkali metals (group 1), the halogens (group 7) and the noble gases (group 0). You describe their physical properties and reactions, explain the trends in reactivity using electronic configurations, and predict the properties of elements you have not studied. Topic 6 is assessed on Paper 2 and builds on atomic structure and the periodic table from Topic 1. Examiners frequently ask for observations when alkali metals react with water, displacement reactions between halogens and halide solutions, and explanations of trends using the distance of the outer shell from the nucleus.

What you need to know

• Group 1 properties Alkali metals are soft, have relatively low melting points and are stored under oil because they react with air and water. They react with water to form a metal hydroxide and hydrogen, for example 2K + 2H2O → 2KOH + H2.
• Group 1 observations and trend Lithium fizzes steadily; sodium melts into a ball and moves around on the surface; potassium reacts violently with a lilac flame. Reactivity increases down the group because the outer electron is further from the nucleus and more easily lost.
• Group 7 properties Chlorine is a pale green gas, bromine is a red-brown liquid and iodine is a dark grey solid that forms a purple vapour. Melting and boiling points increase down the group. Chlorine bleaches damp blue litmus paper (it may turn red first).
• Group 7 reactions Halogens react with metals to form metal halides and with hydrogen to form hydrogen halides, which dissolve in water to form acidic solutions. Reactivity decreases down the group because it is harder for the atom to gain an electron when the outer shell is further from the nucleus.
• Displacement (redox at Higher tier) A more reactive halogen displaces a less reactive one from an aqueous solution of its halide, for example Cl2 + 2KBr → 2KCl + Br2. Higher tier only: these are redox reactions; the halogen is reduced (gains electrons) and the halide ion is oxidised.
• Group 0 Noble gases are chemically inert because they have full outer shells. Uses depend on low density (helium in balloons), being inert (argon in filament lamps and as a shielding gas in welding) or glowing in electrical discharge (neon in signs). Boiling point and density increase down the group.

Common mistakes in Topic 6: Groups in the Periodic Table

• Explaining group 1 trends by saying 'there are more electrons'. Talk about increasing distance and shielding, which weaken the attraction for the outer electron.
• Saying halogen reactivity increases down the group. It decreases.
• Describing iodine as purple solid. Iodine is a dark grey solid with a purple vapour.
• Writing displacement equations with the less reactive halogen displacing the more reactive one, for example iodine displacing chlorine.
• Saying noble gases are unreactive because they have 8 outer electrons. Helium has 2; the point is a full outer shell.

Try three Topic 6: Groups in the Periodic Table exam-style questions