The atomic structure of carbon. Image credit

The atomic structure of carbon. Image credit

ZIMSEC O Level Combined Science Notes: Structure of atoms: protons,electrons and neutrons

Protons and neutrons

  • The protons are the positive charge in the nucleus of an atom
  • The neutrons are also in the nucleus but they have no charge
  • The mass of neutrons is the same as that of protons
  • Neutrons and protons have the same mass
  • Neutrons have no charge
  • Protons have a positive charge
  • The particles in the nucleus i.e the protons and the neutrons are known as nucleons
  • The number of nucleons is known as the nucleon number


  • Electrons have a negative charge
  • They circle around the nucleus in fixed orbits called electronic shells
  • The mass of an electron is much smaller than that of a proton


  • Atoms have no charge
  • They are electrically neutral
  • This is because the number of protons and electrons is always equal
  • The negative and positive charges cancel each other

To access more topics go to the Combined Science Notes page.

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