Atomic Structure

This lesson covers the structure of the atom and the sub-atomic particles within it, as required by AQA GCSE Chemistry specification (5.1.1). Understanding atomic structure is fundamental to chemistry — it explains why elements behave the way they do, how they bond, and why the periodic table is arranged the way it is.

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The Structure of an Atom

An atom consists of a central nucleus surrounded by electrons that orbit in shells (energy levels). The nucleus is extremely small compared to the overall size of the atom.

Part of the Atom	Description
Nucleus	Found at the centre of the atom. Contains protons and neutrons. Very small and dense. Positively charged overall.
Electron shells	Regions around the nucleus where electrons are found. Electrons orbit the nucleus at specific energy levels (shells).

The radius of an atom is approximately 1 x 10^-10 m (0.1 nm). The radius of the nucleus is about 1 x 10^-14 m — roughly 10,000 times smaller than the atom itself. This means that most of an atom is empty space.