Protons, Neutrons & Electrons (Edexcel GCSE Physics)

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Relative Mass & Charge

Properties of Sub-atomic particles

  • The different particles that make up atoms have different properties
  • Relative mass is a way of comparing particles. It is measured in atomic mass units (amu)
  • A relative mass of 1 is equal to mass of 1.67 × 10-27 kg
  • Charge can be positive or negative
  • Relative charge is, again, used to compare particles
  • The fundamental charge is equal to the size of the charge on a proton and an electron, however the electron's charge is negative
  • The properties of each of the particles are shown in the table below:

Particles in the atom, downloadable GCSE Physics revision notes

Positrons

  • A positron is the antiparticle of an electron
  • It has the same mass as an electron, and the same size of charge, however it has a positive charge
  • Positrons can be produced during nuclear beta-plus decay
    • a proton spontaneously changes into a neutron and a positron

  • They only exist in normal conditions for a fraction of a second before they react with electrons and are destroyed

Electrons & Protons

  • Although atoms contain particles of different charge, the total charge within an atom is zero
    • This is because the number of electrons is equal to the number of protons

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

A Lithium atom has three protons, four neutrons and three electrons

  • The following table sets out the calculation of the total charge in the Lithium atom:

Total Charge Calculation Table

Charge calculation, downloadable IGCSE & GCSE Physics revision notes

  • If an atom loses electrons, then it is said to be ionised

Worked example

A nucleus of carbon-12 is shown below.Carbon 12 Nucleus Worked Example, downloadable IGCSE & GCSE Physics revision notesHow many electrons are there in an atom of carbon-12?

Step 1: Count the number of protons in the carbon nucleus

    • There are 6 protons in the carbon atom

Step 2: Determine the number of electrons

    • Remember, the number of electrons in an atom is equal to the number of protons
    • Therefore there must be 6 electrons in the carbon atom

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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.