Electronic Structure

This lesson covers the electronic structure (electron configuration) of atoms, as required by AQA GCSE Chemistry specification (5.1.1). The arrangement of electrons in an atom determines how that element reacts, what type of bonds it forms, and where it sits in the periodic table. Understanding electronic structure is essential for explaining reactivity, bonding, and the properties of elements.

---

Electron Shells (Energy Levels)

Electrons occupy 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
3rd shell	8 (at GCSE level)	Furthest (for first 20 elements)

Rules for Filling Electron Shells