Cambridge IGCSE Chemistry 8 The Periodic Table Exam Questions

About Cambridge IGCSE Chemistry 8 The Periodic Table

The Periodic Table topic in Cambridge IGCSE Chemistry 0620 explains how elements are arranged by proton number and how this predicts their properties. You need to describe the change from metallic to non-metallic character across a period, the trends in Group I (lithium, sodium and potassium) and Group VII (chlorine, bromine and iodine), the general properties of transition elements and why noble gases are unreactive. Extended candidates also cover variable oxidation numbers in transition elements. It relies on electronic configuration from atomic structure. Examiners love prediction questions about unfamiliar elements such as rubidium or astatine, halogen displacement equations and observations, and Group I reactions with water.

What you need to know

• 8.1 Arrangement Elements are arranged in order of increasing proton number. Groups are vertical columns of elements with the same number of outer electrons; periods are rows. Across a period, elements change from metallic to non-metallic.
• 8.2 Group I Lithium, sodium and potassium are soft, have low densities and low melting points, which decrease down the group. They react with cold water to form an alkaline hydroxide solution and hydrogen, e.g. 2Na + 2H2O → 2NaOH + H2. Reactivity increases down the group.
• 8.3 Group VII Halogens are diatomic. At room temperature chlorine is a pale yellow-green gas, bromine a red-brown liquid and iodine a grey-black solid. Density increases and reactivity decreases down the group.
• 8.3 Displacement A more reactive halogen displaces a less reactive halide from aqueous solution, for example Cl2 + 2KBr → 2KCl + Br2, turning the solution orange-brown. These are redox reactions.
• 8.4 Transition elements Transition elements have high densities and high melting points, form coloured compounds and, as elements and compounds, act as catalysts. Extended candidates know they have ions with variable oxidation numbers, such as iron(II) and iron(III).
• 8.5 Noble gases Group VIII elements are unreactive, monatomic gases because they have full outer shells, so they do not need to gain, lose or share electrons.
• Explaining trends (Supplement) Down Group I, the outer electron is further from the nucleus and more shielded, so it is lost more easily. Using the trends, you should predict properties of other elements in a group from given data.

Common mistakes in 8 The Periodic Table

• Mixing up chlorine and chloride. Chlorine is the element Cl2; chloride is the ion Cl- in a compound.
• Saying the halogens get more reactive down the group. Reactivity decreases from fluorine to iodine.
• Saying a less reactive halogen displaces a more reactive one. Iodine cannot displace chloride ions; only a more reactive halogen displaces a less reactive one.
• Describing sodium as reacting with water to form sodium oxide. The products are sodium hydroxide and hydrogen.
• Giving the wrong colours for the halogens. Learn chlorine pale yellow-green gas, bromine red-brown liquid, iodine grey-black solid.

Try three 8 The Periodic Table exam-style questions