3.2.2.3 Particles and Radiation: Energy levels and photon emission

Question 1

What can be used as evidence for transitions between discrete energy levels in atoms?

Answer 1

Line spectra

Question 2

What is a line emission spectrum?

Answer 2

A series of bright lines against a black background. Each line corresponds to a particular wavelength emitted by the source.

Question 3

Why do line spectra provide evidence that electrons in atoms exist in discrete energy levels?

Answer 3

Atoms can only emit photons with energies equal to the difference between two energy levels, since only certain photon energies are allowed, you only see the corresponding wavelengths in the line spectrum.

Question 4

What happens in continuous spectra?

Answer 4

All wavelengths are allowed because electrons are not confined to energy levels in the object producing the continuous spectrum. The electrons are not bound to atoms and are free

Question 5

How do you get a line absorption spectrum?

Answer 5

When light with a continuous spectrum of energy (white light) passes through a cool gas.

Question 6

What is the difference between line absorption spectra and line emission spectra?

Answer 6

Absorption (from cool gas) - black lines on continuous spectrum
Emission (from excited gas) - spectra against a black background
- the black lines from the absorption spectrum match with the bright lines in the emission spectrum