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AQASpec 4.1Foundation & Higher~30 min

Atomic Structure & Periodic Table

Chemistry · Topic revision workspace

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Topic overview

What you need to know

Atomic Structure & Periodic Table is a key part of GCSE Chemistry. Link particles, structure and energy changes to the observations and calculations you may be given. The smallest part of an element that can exist. Made up of protons, neutrons (in the nucleus), and electrons (in shells). A positively charged subatomic particle found in the nucleus. Relative mass = 1, relative charge = +1. A neutral subatomic particle found in the nucleus. Relative mass = 1, relative charge = 0.

Exam tip

Balance equations, show units in calculations and connect macroscopic observations to particles.

Revision notes

Core ideas

Secure these ideas first. Say each definition in your own words, then connect it to the topic overview.

  • Atom: The smallest part of an element that can exist. Made up of protons, neutrons (in the nucleus), and electrons (in shells).
  • Proton: A positively charged subatomic particle found in the nucleus. Relative mass = 1, relative charge = +1.
  • Neutron: A neutral subatomic particle found in the nucleus. Relative mass = 1, relative charge = 0.
  • Electron: A negatively charged subatomic particle orbiting the nucleus in energy levels (shells). Relative mass ≈ 0 (1/1836), charge = −1.

Revision notes

Apply it in the exam

The exam will rarely ask for an isolated definition. Practise selecting the right idea and using it as part of a complete explanation or method.

  • Atomic Number: The number of protons in the nucleus of an atom. It defines the element and equals the number of electrons in a neutral atom.
  • Mass Number: The total number of protons and neutrons in the nucleus. Mass number = protons + neutrons.
  • Isotope: Atoms of the same element with the same number of protons but different numbers of neutrons.
  • Electronic Configuration: The arrangement of electrons in energy levels. The first shell holds 2, the second holds 8, the third holds 8. E.g. sodium = 2,8,1.

Core knowledge

Key facts for Atomic Structure & Periodic Table

1

Atom

The smallest part of an element that can exist. Made up of protons, neutrons (in the nucleus), and electrons (in shells).

2

Proton

A positively charged subatomic particle found in the nucleus. Relative mass = 1, relative charge = +1.

3

Neutron

A neutral subatomic particle found in the nucleus. Relative mass = 1, relative charge = 0.

4

Electron

A negatively charged subatomic particle orbiting the nucleus in energy levels (shells). Relative mass ≈ 0 (1/1836), charge = −1.

5

Atomic Number

The number of protons in the nucleus of an atom. It defines the element and equals the number of electrons in a neutral atom.

6

Mass Number

The total number of protons and neutrons in the nucleus. Mass number = protons + neutrons.

7

Isotope

Atoms of the same element with the same number of protons but different numbers of neutrons.

8

Electronic Configuration

The arrangement of electrons in energy levels. The first shell holds 2, the second holds 8, the third holds 8. E.g. sodium = 2,8,1.

Active recall

Close the notes and answer these

  1. 1.Without looking, explain atom and give one example or consequence.
  2. 2.Without looking, explain proton and give one example or consequence.
  3. 3.Without looking, explain neutron and give one example or consequence.
  4. 4.Without looking, explain electron and give one example or consequence.

Content reviewed 23 July 2026 against the current linked specification.

Finished learning?

Mark the notes complete, then test what you can recall.

Official AQA specification
Next topicBonding, Structure & Properties