Atomic Structure

This lesson covers the internal structure of the atom — the three sub-atomic particles and how they are arranged — as required by the Edexcel GCSE Combined Science specification (1SC0). You need to know the relative mass and charge of protons, neutrons and electrons, and be able to use atomic number and mass number to determine the number of each particle in any atom.

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Sub-Atomic Particles

Atoms are made of three types of sub-atomic particle: protons, neutrons and electrons.

Sub-Atomic Particle	Relative Mass	Relative Charge	Location
Proton	1	+1	Nucleus
Neutron	1	0	Nucleus
Electron	Very small (≈ 1/1836)	−1	Electron shells (orbiting the nucleus)

Key Points