Home · A-Level Chemistry 9701 · Chemical periodicity of elements in Period 3 · Chemical periodicity of other elements · Practice
AS · Practice questions · Chemical periodicity of other elements

Name the mystery element.

Six original Cambridge-style questions on chemical periodicity: identifying elements from data and predicting the properties of other elements.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Combine clues; never rely on one.

01
Analysis
[3 marks]

Element A: m.p. 660 °C, good conductor, oxide reacts with both HCl and NaOH, chloride gives pH 3 in water. Identify A and explain each piece of evidence.

  • A is aluminium. ✓
  • Moderate melting point and good conductivity: giant metallic structure. ✓
  • Amphoteric oxide and partly hydrolysed chloride: aluminium's intermediate position in Period 3. ✓
02
Analysis
[2 marks]

The first five ionisation energies of element B are 578, 1817, 2745, 11 577 and 14 842 kJ mol−1. Deduce the group of B and the formula of its oxide.

  • The big jump is between the 3rd and 4th, so B has three outer electrons: Group 13. ✓
  • Its oxide has the formula X2O3; B is aluminium, so Al2O3. ✓
03
Analysis
[3 marks]

Element C forms a white solid oxide that dissolves in water to give pH 2, and a chloride CCl5. Identify C, and write equations for its oxide and chloride reacting with water.

  • C is phosphorus (oxidation number +5). ✓
  • P4O10 + 6H2O → 4H3PO4. ✓
  • PCl5 + 4H2O → H3PO4 + 5HCl. ✓
04
Explain
[2 marks]

Predict, with a reason, whether GeO2 is more or less acidic than SiO2.

  • Less acidic (GeO2 is amphoteric). ✓
  • Metallic character increases down Group 14, so the oxide becomes more basic. ✓
05
Explain
[2 marks]

Suggest why first ionisation energy drops from nitrogen to oxygen in Period 2.

  • Oxygen's electron is removed from a 2p orbital containing a pair of electrons. ✓
  • Repulsion between the paired electrons makes it easier to remove, as with P and S in Period 3. ✓
06
Analysis
[2 marks]

Element D has m.p. −101 °C, does not conduct, and its hydride dissolves in water to give a strongly acidic solution. Identify D and its structure.

  • D is chlorine. ✓
  • Simple molecular Cl2, held by weak id-id forces; HCl is a strong acid in water. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.