1. Interpretation of Hydrogen Emission Spectra

2. White Light Spectrum (Wide Range of Colors and hence Energies of light)

3. Spectral lines of Helium (left) and Neon (right)

4. Hydrogen Emission Spectra Experiment – Experimental Observations
Energy added in the form of heat, electricity or light → only certain specific colors of light are emitted

5. Interpretation of Hydrogen Line Spectra- Experimental Observations
Since ONLY CERTAIN SPECIFIC COLORS OF LIGHT ARE EMITTED, ONLY CERTAIN SPECIFIC FREQUENCIES AND WAVELENGTHS ARE EMITTED
Longer wavelengths – like red, have lower energy
Shorter wavelengths – like blue have higher energy
Specific colors = ONLY SPECIFIC ENERGIES OF LIGHT ARE EMITTED

6. Bohr Model
If no restrictions on electrons’ energy and motion e- would pulled into nucleus- this does not happen; therefore there must be restrictions.
Quantized- means restricted: only certain, specific values are possible
Analogies:
Nonquantized = ramp
Quantized = stairs

7. Link to Hydrogen model’s phet

8. Postulates of Bohr model
Electrons can have only certain specific values of energy.
Electrons travel in fixed, circular orbits*
When an electron absorbs the exact difference in energy between 2 levels it makes a quantum leap up
When an electron makes a quantum leap down it releases the exact difference in energy between two levels.
* = we no longer believe this postulate

9. Bohr model of Atom
Historically important – first model of atom to introduce concept of quantized energy levels to explain hydrogen emission spectral lines
Model was unable to explain all details hydrogen spectrum and very poorly predicts spectra of heavier elements
Fatal flaw = oversimplified: e- don’t travel in fixed circular orbits

10. Link to Electron Orbits

11. Interpretation of Experiment
Energy added to atoms is absorbed by ELECTRONS.
Electron absorbs specific quantity of energy, it makes a quantum leap from its lowest energy GROUND state to higher energy EXCITED state.

12. Quantum Leaps: Ground → Excited
Add Energy electron = ↑
n = 3 ___________ excited state
n=2 ___________ excited state
n= ↑ ____________ ground state

13. Quantum Leaps: Ground → Excited
Add Energy electron = ↑
n = 3 ___________ excited state
n=2 ↑ ___________ excited state
n= ____________ ground state

14. Quantum Leaps: Ground → Excited
Add Energy electron = ↑
n = 3 ___________ excited state
n=2 ↑ ___________ excited state
n= ____________ ground state

15. Back Page
Electrons CANNOT remain in an excited state for any significant time period.
Electron in excited state returns to the ground state by emitting a specific amount of energy in the form of LIGHT.
Because only certain specific jumps from excited to ground state are possible, only certain specific energies and hence colors of light can be emitted.

16. Quantum Leaps: Excited → Ground
Release of Light
n = 3 ___________ excited state
n=2 ↑ ___________ excited state
n= ____________ ground state

17. Quantum Leaps: Excited → Ground Release of Light
n = 3 ___________ excited state
n=2 ___________ excited state
n=1 ↑ ____________ ground state

18. Link to Hydrogen Emission Spectrum Animation

19. Link to Neon light PhEt applet

20. Link to lasers phet

21. Sodium Line Emission Spectrum