Rutherford's Interpretation

• Most of the atom's mass is concentrated in a small volume at the centre of the atom i.e. the nucleus.
• The nucleus must be positively charged because it repels positively charged alpha particles.

Using Coulomb's law of force and Newton's Laws of motion the pattern can be explained. By testing foils of different elements he showed that the magnitude of the charge of the nucleus is +Ze where e is the charge of an electron and Z is the atomic number.The size of the nucleus can also be estimated. For a foil n layers of atoms thick that deflects 1 in 10,000 alpha particles, the probability of deflection by each layer is 1 in 10,000n and depends on the ratio of cross-section area of nucleus (π(d/2)²) to atom (π(D/2)²) So d² = D² / 10,000n