Structure of the atom and atomic spectra

Learning objectives

Describe the Geiger–Marsden–Rutherford alpha-scattering experiment, and explain how the small fraction of alpha particles scattered through large angles provides evidence for a tiny, dense, positively charged nucleus

Use nuclide notation to state the numbers of protons, neutrons and nucleons in an atom or ion, and define isotopes as nuclides of the same element with different neutron numbers

Explain discrete line emission and absorption spectra as evidence for discrete atomic energy levels, and relate the energy of an emitted or absorbed photon to the transition using E = hf = hc/λ

(HL) Apply the Bohr model for hydrogen, E = −13.6/n² eV, to calculate the wavelengths of spectral lines and the ionisation energy of the atom from the ground state

(HL) Apply the Bohr quantisation of angular momentum, mvr = nh/2π, to the electron orbits of hydrogen, and calculate the distance of closest approach of an alpha particle in a head-on collision by equating its kinetic energy to the electric potential energy

(HL) Estimate nuclear radius from R = R₀A^(1/3), show that nuclear density is approximately the same for all nuclides, and explain how the departure from Rutherford scattering at high energies gives a measure of nuclear size

Describe the role of the strong nuclear force in binding nucleons together over a very short range, and explain why the electrostatic repulsion between protons limits the size of stable nuclei