Explain how the discovery of the neutron changed scientists' understanding of atomic structure, and state the relative charge of a neutron.

Edexcel A-Level Chemistry (9CH0) — 1.1 Atomic structure · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Early models of the atom suggested that the nucleus contained only protons. In 1932, James Chadwick discovered a new subatomic particle.

Model answer (5 marks)

The neutron is a neutral particle, having no charge.
Neutrons are found in the nucleus together with protons.
Because neutrons add mass but no charge, atoms of the same element can have different masses.
Atoms of the same element with different numbers of neutrons are called isotopes.
The mass number of an atom equals the total number of protons plus neutrons in its nucleus.

Examiner tips

  • Use the word "neutral" for charge; mention nucleus; link neutrons to mass variation; define isotopes; state mass number formula

Common mistakes

  • Saying the neutron has a small charge; confusing neutrons with electrons; forgetting to mention the nucleus; not defining isotopes; omitting the mass number equation

Mark scheme (5 marks)

  1. States that the neutron has no charge / is neutral / relative charge of zero
  2. States that neutrons are found in the nucleus
  3. Explains that the existence of neutrons accounts for why atoms of the same element can have different masses
  4. States that isotopes are atoms of the same element with different numbers of neutrons (or different mass numbers)
  5. Explains that the mass number equals the total number of protons plus neutrons in the nucleus

Key terms in this question

neutron

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