Electronic Configuration

This lesson covers how electrons are arranged in atoms, as required by AQA GCSE Combined Science Trilogy (8464, Chemistry 4.1.1). Electronic configuration determines how an element reacts and where it sits in the periodic table. Understanding this topic is essential for explaining bonding, reactivity trends and the periodic table.

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Energy Levels (Electron Shells)

Electrons occupy energy levels (also called shells) around the nucleus. The shells are filled from the innermost shell (closest to the nucleus, lowest energy) outwards.

Energy Level (Shell)	Maximum Electrons
1st shell	2
2nd shell	8
3rd shell	8 (at GCSE level)

Exam Tip: At GCSE, the 3rd shell holds a maximum of 8 electrons. In reality it can hold 18, but the additional electrons fill 3d sub-shells, which is an A-level topic. AQA will only test up to the first 20 elements.

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Rules for Filling Electron Shells