Q94 · Practice questionComplex familiar5 marks
QUESTION 94 (5 marks)
Contrast Rutherford’s and Bohr’s atomic models, and explain why Bohr’s model can account for discrete hydrogen emission lines whereas Rutherford’s model cannot.
WORKED SOLUTION
5 marksPractice marking scheme
ANSWER
Rutherford proposed a small positive nucleus with orbiting electrons but no quantised electron energies. Bohr retained a nuclear atom but restricted electrons to discrete stationary energy levels; photons are emitted with when electrons move between levels, giving discrete spectral lines.
Worked solution
Rutherford’s model established that positive charge and most mass are concentrated in a small nucleus, with electrons outside it. However, classical orbiting electrons in that model have no prescribed discrete energies, so it does not naturally predict a set of discrete photon energies. Bohr introduced allowed stationary electron states with quantised energies/angular momentum. An electron can change between these states only by absorbing or emitting a photon whose energy equals the state separation, . Because only particular values are allowed, only particular wavelengths occur in the hydrogen spectrum.
Describes Rutherford nuclear model.
Identifies lack of quantised energy in Rutherford model.
Describes Bohr quantised stationary states.
Links transitions to photon energy.
Links discrete energy differences to line spectrum.
Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
View the QCAA syllabusHow many marks did you earn?
Compare your working with the guide above.