Development of the periodic table — AQA GCSE Chemistry
Test yourself on Development of the periodic table with AQA GCSE practice questions.
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Development of the periodic table explained
The periodic table developed through several stages.
Read the full explanation
Early chemists such as Newlands and Döbereiner noticed patterns, but Mendeleev produced the version that shaped later work. He arranged elements mainly by relative atomic weight, placed elements with similar properties into groups, and left gaps for elements he predicted were undiscovered. When gallium and germanium were later found with properties close to his predictions, confidence in the table grew. Later work on atomic structure showed that proton number, not atomic weight, gives the correct order, and this resolved anomalies such as argon before potassium. The modern table arranges elements by increasing proton number, with groups showing similar properties and periods showing repeating trends.
Your focus
- Sequence the main stages in the development of the periodic table.
- Explain how Mendeleev used gaps and predictions.
- State why the modern table uses proton number.
Development of the periodic table exam tips
Marking Points
- Describe early attempts to find patterns among elements, including ordering by relative atomic weight.
- Describe Mendeleev arranging elements by atomic weight and grouping those with similar properties.
- Describe Mendeleev leaving gaps and predicting properties of undiscovered elements.
- Describe how later discovery of predicted elements supported the table.
- Describe the modern change to ordering by proton number, which resolved anomalies.
Examiner Tips
- 💡Use a clear sequence: early patterns, Mendeleev's table, predictions, later proton-number ordering.
- 💡Name at least one predicted element, such as gallium or germanium, to support the description.
- 💡Keep the account chronological so the examiner can follow the development.
Common Mistakes
- Crediting Mendeleev with ordering by proton number; correct this by stating he used atomic weight and that proton number came later.
- Saying Mendeleev left gaps because he had no data; correct this by explaining the gaps were for elements not yet discovered.
- Treating the periodic table as a single invention; correct this by describing it as a sequence of improvements over time.