Atomic Model

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Atomic Model - Example

An atom has a small, positively-charged nucleus surrounded by orbiting negatively-charged electrons.

Size of Atoms vs Nucleus

Atoms have a radius of about 1 × 10-10 metres. However, the nucleus of atoms are even smaller.


  • If an atom was the size of Wembley Stadium, then...


  • ...its nucleus would be the size of a garden pea!

The Charges and Masses of Sub-Atomic Particles

The 3 different sub-atomic particles (protons, neutrons and electrons) have different relative charges and masses. Atoms have no overall charge (are neutral). In an atom, these charges all cancel each other out.

Illustrative background for ProtonsIllustrative background for Protons ?? "content


  • Protons have a relative charge of +1.
    • In SI units, this is +1.60 × 10-19C.
  • They are found in the nucleus.
  • An element’s atomic number is the number of protons it possesses.
    • All atoms of the same element have the same number of protons.
  • Protons have a relative atomic mass of 1.
    • In SI units, this is 1.67 × 10-27kg.
Illustrative background for ElectronsIllustrative background for Electrons ?? "content


  • Electrons have a relative charge of -1.
    • In SI units, this is -1.60 × 10-19C.
  • They are found in fixed orbits around the nucleus.
  • In any atom, the total number of negative electrons equals the number of positive protons, meaning atoms have no overall electric charge.
  • Electrons have a relative atomic mass of 1/2000.
    • In SI units, this is 9.11 × 10-31kg.
Illustrative background for NeutronsIllustrative background for Neutrons ?? "content


  • Neutrons have a relative charge of 0 - they are neutral.
  • Like protons, they are found in the nucleus.
  • Neutrons have a relative atomic mass of 1 (the same as a proton).

Jump to other topics

1Measurements & Errors

2Particles & Radiation


4Mechanics & Materials


6Further Mechanics & Thermal Physics (A2 only)

7Fields & Their Consequences (A2 only)

8Nuclear Physics (A2 only)

9Option: Astrophysics (A2 only)

10Option: Medical Physics (A2 only)

11Option: Engineering Physics (A2 only)

12Option: Turning Points in Physics (A2 only)

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