The Periodic Table

This lesson covers the periodic table — its history, organisation and significance — as required by AQA GCSE Chemistry specification (5.1.2). The periodic table is one of the most important tools in chemistry. It organises all known elements according to their atomic structure and allows chemists to predict the properties and reactions of elements.

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Early Attempts to Classify Elements

Before the modern periodic table was developed, scientists attempted to organise elements in various ways. You need to know the key historical developments:

John Newlands (1864) — Law of Octaves

• Newlands arranged the known elements in order of atomic weight (relative atomic mass).
• He noticed that every eighth element had similar properties — he called this the Law of Octaves (by analogy with musical octaves).
• Problems: Newlands' table only worked for the first 16 elements. He forced some elements into groups where they did not fit. He did not leave gaps for undiscovered elements. His ideas were ridiculed by the scientific community at the time.

Dmitri Mendeleev (1869) — The First Successful Periodic Table