The Periodic Table

This lesson covers the history and structure of the periodic table as required by the Edexcel GCSE Chemistry specification (1CH0), Topic 1: Key Concepts in Chemistry. You need to understand how Mendeleev developed the periodic table, how the modern table is arranged, and the key features of groups and periods.

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Early Attempts to Classify Elements

In the 19th century, scientists tried to organise the known elements. At this time, only about 60 elements had been discovered, and scientists knew little about atomic structure.

Newlands' Law of Octaves (1864)

John Newlands arranged the known elements in order of atomic weight (relative atomic mass). He noticed that every eighth element had similar properties — like the octaves in music.

Problems with Newlands' approach:

• It only worked for the first 20 or so elements.
• He forced elements into groups where they did not fit.
• He did not leave any gaps for undiscovered elements.
• His work was not taken seriously by other scientists at the time.

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Mendeleev's Periodic Table (1869)