Light as a Wave

Emission Line Spectra

• Since every element has a different set of atomic orbital energies, the emission line spectrum of every element is different. They are as unique as fingerprints!

• Blackbody Spectra

• Emission Line Spectra

Absorption Line Spectra

• An object (like a star) emits a hot blackbody spectrum. Somewhere between you and the star (like on the outside of the star) is some cooler gas. That gas can absorb the photons which correspond to the atom’s energy levels. The result is an absorption spectrum.

• Absorption Line Spectrum from the Sun

• Continuous Spectrum

• Emission Spectrum

• Absorption Spectrum

Continuous, Emission, and Absorption Spectra

Question 1

Question 2

Question 2: (cont.)

Question 3:

• The following is a simplified energy level diagram for atomic hydrogen.

• State the ionisation energy of atomic hydrogen.

• 13.6 eV

Question 3: (cont.)

• Energy is needed to raise the electrons to an energy of 0 eV, so it must start negative.
• OR
• Energy is given out when the electrons move to the ground state, so energy now less than 0, i.e. negative
• OR
• the ground state is the most stable energy level of the electrons and must be less than 0, i.e. negative

• Account for the labelling of the energy levels with negative numbers.

Question 3: (cont.)

• Calculate the wavelength of the photon emitted when an electron moves from the –1.51 eV energy level to the –3.40 eV energy level.

Question 3: (cont.)

• Describe how you would produce a line spectrum of atomic hydrogen in a laboratory.

• Source – hydrogen discharge tube/hydrogen lamp/low p hydrogen with high V across (1)
• viewed through diffraction grating or prism.