Protons, Neutrons & Electrons (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award): Physics): Revision Note

Relative charge

• 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 

$\mathrm{proton}=\frac{1.6\times {10}^{-19}\mathrm{C}}{1.6\times {10}^{-19}\mathrm{C}}=+1$

• The relative charge of an electron is

$\mathrm{electron}=\frac{-1.6\times {10}^{-19}\mathrm{C}}{1.6\times {10}^{-19}\mathrm{C}}=-1$

• The relative charge of a neutron is

$\mathrm{neutron}=\frac{0\mathrm{C}}{1.6\times {10}^{-19}\mathrm{C}}=0$

Table of relative charges

Nuclear charge

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: 

$\mathrm{nuclear}\mathrm{charge}=\mathrm{number}\mathrm{of}\mathrm{protons}\mathrm{in}\mathrm{the}\mathrm{nucleus}\times \mathrm{relative}\mathrm{charge}\mathrm{of}\mathrm{a}\mathrm{proton}$

• An element of carbon has a proton number of 6

  • So the relative charge of carbon is 6 × (+1) = 6