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

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:

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

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

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