1. Interpretation of Hydrogen Emission Spectra

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

3. Hydrogen Emission Spectrum

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

5. Mercury spectrum

6. Concept of Quantized
Quantized – restricted values; only certain specific values are allowed.
Analogies:
Nonquantized: Ramp
Quantized: Stairs, ladder

7. Concept of Absorbance vs. Emission Spectrum

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

9. 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

10. Bohr Model (1913 – Niels Bohr)
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
HW 8-2
Quantized = stairs
Link to Hydrogen model’s phet

11. Postulates of Bohr model
HW 8-2
Electrons can have only certain specific values of energy.
Electrons travel in fixed, circular orbits*
(* = we no longer believe this postulate)
(QUANTIZED ENERGIES)

12. Postulates of Bohr model
GROUND STATE = LOWEST ENERGY STATE
EXCITED STATE= HIGHER ENERGY STATE
Energy absorbed
Energy Released as light
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 as light

13. Link to Electron Orbits

14. 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.

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

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

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

18. 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.
HW 8-2, #6

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

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

21. Which color of light is associated with which Quantum Jump?
We observed the lines of color in the hydrogen spectrum red, teal, and violet.
These different colors were released as a result of 3 different jumps between levels:
5 → 2, 4 → 2 and 3 → 2. Which jump corresponds to which color of light emission and how do you know?
Link to Hydrogen Emission Spectrum Animation

23. How can all of these jumps be happening at the same time?
Each of the different colors in the hydrogen spectrum is the result of different quantum leaps. A hydrogen atom has one electron. How can all of these jumps being happening at once? How can all of these different colors of light be emitted at the same time?

24. Link to lasers phet
The tube contains an enormous population of hydrogen atoms – trillions and trillions of atoms
Within the population every possible transition that could take place does

25. Why can we see only 3 lines of color for the hydrogen spectrum?
Each quantum leap from excited back to ground should release energy in the form of light e.g. 2→ 1, 3 → 1, 4 → 3, etc. Yet we only see 3 colors of light from the 5 → 2, 4 → 2 and 3 → 2 transitions. Why don’t we see more colors of light?

26. Link to Neon light PhEt applet
Most of the transitions release light outside the visible range – in the infrared or ultraviolet range.