Atomic Structure (Edexcel GCSE Physics)

Protons, Neutrons & Electrons

• Atoms are the building blocks of all matter

• They are incredibly small - for instance, about one hundred million atoms could fit side by side across your thumbnail

• Atoms have a tiny, dense nucleus at their centre, with electrons orbiting around the nucleus

• The nucleus is made up of protons and neutrons

• The radius of the nucleus is over 10,000 times smaller than the whole atom, but it contains almost all of the mass of the atom

Diagram showing the structure of a Lithium atom. If drawn to scale then the electrons would be around 100 metres away from the nucleus!

Parts of the Atom

• The nucleus contains:

  • Protons - positively charged particles with a relative atomic mass of one unit

  • Neutrons – no charge, and also with a relative atomic mass of one unit

• Almost all of the atom is empty space, but moving around the nucleus there are:

  • Electrons – negative charge with almost no mass (1/2000 the mass of a proton or neutron)

• The properties of each of the particles are shown in the table below: