Protons, Neutrons & Electrons (Edexcel GCSE Combined Science) : Revision Note

Ashika

Author

Ashika

Last updated

Did this video help you?

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 notes

How many electrons are there in an atom of carbon-12?

Answer:

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

👀 You've read 1 of your 5 free revision notes this week
An illustration of students holding their exam resultsUnlock more revision notes. It's free!

By signing up you agree to our Terms and Privacy Policy.

Already have an account? Log in

Did this page help you?

Ashika

Author: Ashika

Expertise: Physics Content Creator

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.

Download notes on Protons, Neutrons & Electrons