Protons, Neutrons & Electrons (CIE IGCSE Physics)

• Charge can be positive or negative
• Protons, neutrons and electrons have different properties and different charges
  • Protons have a positive charge
  • Electrons have a negative charge
  • Neutrons have no charge
• Relative charge can be used to compare these properties
  • Relative charge is the ratio of the charge of a particle compared to the fundamental charge 
  • Because relative charge is a ratio, it has no units
• Fundamental charge is equal to the magnitude of the charge on a proton and an electron = 1.6 × 10⁻¹⁹ C
• The relative charge of a proton is 

• The relative charge of an electron is

• The relative charge of a neutron is

Table of relative charges

Extended tier only

• Nuclear charge is the relative charge of the nucleus
• This is determined by the proton number of the atom
• Relative charge is calculated by: 

• An element of carbon has a proton number of 6
  • So the relative charge of carbon is 6 × (+1) = 6

Extended tier only

• Nuclear mass or the relative mass of an atom, is the relative mass of the nucleus
  • This is because the mass of electrons orbiting the nucleus is negligible
• A relative mass of 1 = 1.67 × 10^-27 kg
• The relative mass of an atom is determined by the nucleon number of the atom
• It is calculated by: 

• An element of carbon has a nucleon number of 12
  • So the relative mass of carbon is 12 × 1 = 12 atomic mass units or amu

Table of relative mass

Particle	Relative mass
Proton	1
Neutron	1
Electron	negligible