C1 - Atomic Structure GCSE AQA Chemistry Summary Notes

C1 – Atomic Structure
GCSE Chemistry Guide
1. Atoms and Elements

What is an Atom?
An atom is the smallest particle of an element that can exist. All substances are made from
atoms.

- Nucleus: Contains protons and neutrons.
- Electron Shells: Contain electrons orbiting the nucleus.

Subatomic Particles
Particle Charge Relative Mass
Proton +1 1
Neutron 0 1
Electron -1 ~1/1836




2. Elements
An element contains only one type of atom.
- Each element has a unique atomic number (number of protons).
- The mass number = protons + neutrons.

Example:
- Carbon has atomic number 6 and mass number 12.