Electron Configuration

This lesson covers how electrons are arranged in atoms — known as electron configuration — as required by the Edexcel GCSE Chemistry specification (1CH0), Topic 1: Key Concepts in Chemistry. You need to be able to work out the electron configuration of the first 20 elements and understand how it links to an element's position in the periodic table and its chemical properties.

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Electron Shells

Electrons are arranged in shells (also called energy levels) around the nucleus. Each shell can hold a maximum number of electrons:

Shell Number	Maximum Electrons	Distance from Nucleus
1st shell (innermost)	2	Closest
2nd shell	8	Further out
3rd shell	8 (at GCSE level)	Further still
4th shell	2 (for the first 20 elements at GCSE)	Furthest

Rules for Filling Electron Shells