AQA GCSE Chemistry 4.1.2 The Periodic Table Exam Questions

About AQA GCSE Chemistry 4.1.2 The Periodic Table

In AQA GCSE Chemistry section 4.1.2 you learn why the periodic table is arranged the way it is and how electronic structure explains the patterns in it. You study how Mendeleev's table developed from earlier attempts, then the trends in Group 0 (noble gases), Group 1 (alkali metals) and Group 7 (halogens). This topic is examined on Paper 1 and links directly to bonding in 4.2 and reactivity of metals in 4.4. Examiners like questions that ask you to explain a trend in reactivity using shells and outer electrons, write balanced equations for Group 1 and Group 7 reactions and predict properties of unfamiliar elements.

What you need to know

• Arrangement Elements are arranged in order of atomic number. Elements in the same group have the same number of outer shell electrons and so similar chemical properties; the period number equals the number of occupied shells.
• Development of the table Early tables ordered elements by atomic weight and were incomplete. Mendeleev left gaps for undiscovered elements and changed the order of some elements to fit properties; the discovery of isotopes later explained why ordering by atomic weight was not always correct.
• Metals and non-metals Metals are on the left and centre and form positive ions; non-metals are on the right and do not form positive ions.
• Group 0 Noble gases are unreactive because they have a full outer shell (8 electrons, or 2 for helium). Boiling point increases down the group as relative atomic mass increases.
• Group 1 Alkali metals react with oxygen, chlorine and water; with water they form a metal hydroxide and hydrogen. Reactivity increases down the group because the outer electron is further from the nucleus and more easily lost.
• Group 7 Halogens exist as diatomic molecules. Down the group, relative molecular mass, melting point and boiling point increase and reactivity decreases because it is harder to gain an electron. A more reactive halogen displaces a less reactive one from a solution of its salt.

Common mistakes in 4.1.2 The Periodic Table

• Saying Group 1 reactivity increases 'because there are more electrons'. Explain that the outer electron is further from the nucleus with more shielding, so attraction is weaker and the electron is lost more easily.
• Getting the Group 7 trend the wrong way round. Halogen reactivity decreases down the group because the outer shell is further from the nucleus, so an electron is gained less easily.
• Writing halogens as single atoms, for example Cl instead of Cl2, in equations.
• Stating that Mendeleev arranged elements by atomic number. He used atomic weight, but swapped some elements and left gaps based on properties.
• Describing alkali metals reacting with water to form an acid. They form an alkaline hydroxide solution and hydrogen gas.

Try three 4.1.2 The Periodic Table exam-style questions