Quantum Phenomena - discrete energy levels for electrons


(a) Line spectra were observed before they could be explained by theory. We now know that photons of characteristic frequency are emitted when the vapour of an element is bombarded by energetic electrons.

The spectrum of the light emitted contains lines, each of a definite wavelength.

Explain how

• the bombarding electrons cause the atoms of the vapour to emit photons

• the existence of a spectrum consisting of lines of a definite frequency supports the view that atoms have discrete energy levels.

(6 marks)

(b) The ionisation energy of a hydrogen atom is 13.6 eV.

(i) State what is meant by the ionisation energy of hydrogen.

(2 marks)

(ii) Express the ionisation energy of hydrogen in joules, giving your answer to an appropriate number of significant figures.

(3 marks)

(Total 11 marks)