Inside the Atom (Edexcel GCSE Physics)

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Inside the Atom

  • Atoms are the building blocks of all matter
  • Atoms have a tiny, dense, positively charged nucleus at their centre, with negatively charged electrons orbiting around the nucleus
  • 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

Nucleus and electrons, downloadable AS & A Level Physics revision notes

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 Size of the Atom

  • Atoms are incredibly small, with a radius of only 1 × 10-10 m
  • This is 0.0000000001 m when written without standard form
    • This means that about one hundred million atoms could fit side by side across your thumbnail

  • A group of atoms can bond together to make molecules, such as water
    • A water molecule is comprised of two hydrogen atoms and one oxygen atom

Size of molecules, downloadable IGCSE & GCSE Physics revision notes

A 200 ml glass of water will contain approximately 7,000,000,000,000,000,000,000,000 water molecules!

Examiner Tip

There are many different models of the atom. As you progress through the topic you will discover that the atom can be described in many different ways, such as the Plum Pudding Model that is covered later, but for your exam, make sure to only use the model and descriptions described here.

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Ashika

Author: Ashika

Expertise: Physics Project Lead

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.