Development of the periodic table (5.1.2.2) | AQA GCSE Combined Science: Trilogy (8464) — Chemistry — Foundation | KnowledgeSet

Development of the periodic table

Chemistry (Combined Science) · GCSE · AQA · AQA GCSE Combined Science: Trilogy (8464) — Chemistry — Foundation · Specification point · 5.1.2.2 · Atomic structure and the periodic table · The periodic table

Mendeleev's periodic table

Early periodic tables by atomic weight

Predicted elements and the validation of Mendeleev's table

Isotopes and atomic weight anomalies

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5.1.2.2 Development of the periodic table

Content	Key opportunities for skills development
$Before the discovery of protons, neutrons and electrons, scientists attempted to classify the elements by arranging them in order of their atomic weights. The early periodic tables were incomplete and some elements were placed in inappropriate groups if the strict order of atomic weights was followed. Mendeleev overcame some of the problems by leaving gaps for elements that he thought had not been discovered and in some places changed the order based on atomic weights. Elements with properties predicted by Mendeleev were discovered and filled the gaps. Knowledge of isotopes made it possible to explain why the order based on atomic weights was not always correct. Students should be able to describe these steps in the development of the periodic table.$	$WS 1.1, 1.6 Explain how testing a prediction can support or refute a new scientific idea.$

Content

Key opportunities for skills development

Before the discovery of protons, neutrons and electrons, scientists attempted to classify the elements by arranging them in order of their atomic weights. The early periodic tables were incomplete and some elements were placed in inappropriate groups if the strict order of atomic weights was followed. Mendeleev overcame some of the problems by leaving gaps for elements that he thought had not been discovered and in some places changed the order based on atomic weights. Elements with properties predicted by Mendeleev were discovered and filled the gaps. Knowledge of isotopes made it possible to explain why the order based on atomic weights was not always correct. Students should be able to describe these steps in the development of the periodic table.

WS 1.1, 1.6 Explain how testing a prediction can support or refute a new scientific idea.