OxfordAQA International GCSE Chemistry 3.7 Trends within the Periodic Table Exam Questions

About OxfordAQA International GCSE Chemistry 3.7 Trends within the Periodic Table

Trends within the Periodic Table in OxfordAQA International GCSE Chemistry asks you to describe and explain patterns in Group 1 and Group 7, and, in the separate Chemistry course, the properties of transition metals. It builds directly on electronic structure from 3.1 and ionic bonding from 3.2. You need the reactions of the alkali metals with water and non-metals, the reactions of halogens with metals, halogen displacement and the reasons reactivity changes down each group. Examiners often give data on an unfamiliar element such as rubidium or astatine and ask you to predict its properties, and explanations must refer to the outer electron and its distance from the nucleus.

What you need to know

• Group 1 properties Alkali metals have low density; lithium, sodium and potassium float on water. They react with non-metals to form white ionic compounds with 1+ ions that dissolve to give colourless solutions.
• Group 1 with water They react with water to produce hydrogen and a metal hydroxide that dissolves to give an alkaline solution, for example 2Na + 2H2O → 2NaOH + H2. Reactivity increases down the group.
• Group 7 properties Halogens react with metals to form ionic halides containing 1- ions. Melting and boiling points increase down the group and reactivity decreases.
• Halogen displacement A more reactive halogen displaces a less reactive one from an aqueous solution of its salt, for example Cl2 + 2KBr → 2KCl + Br2. Bromine cannot displace chlorine.
• Explaining trends Going down a group the outer electron is in a higher energy level, further from the nucleus. It is lost more easily, so Group 1 reactivity increases; an electron is gained less easily, so Group 7 reactivity decreases.
• Transition metals (separate Chemistry) Found between Groups 2 and 3. They form ions with different charges, coloured compounds and are useful catalysts. Compared with Group 1 they have higher melting points (except mercury), higher densities, greater strength and hardness and are much less reactive.

Common mistakes in 3.7 Trends within the Periodic Table

• Saying Group 1 metals react more down the group because they have more electrons. The outer electron is further from the nucleus and more shielded, so it is lost more easily.
• Saying Group 7 reactivity increases down the group. It decreases, because it becomes harder to gain an electron.
• Writing that a metal hydroxide solution is neutral or acidic. Group 1 hydroxides give alkaline solutions.
• Writing chlorine as Cl in equations. Halogens are diatomic, so use Cl2, Br2 and I2.
• Saying bromine displaces chloride from potassium chloride. A less reactive halogen cannot displace a more reactive one.

Try three 3.7 Trends within the Periodic Table exam-style questions