1. Photons in / Photons out
6.1.2 Energy Levels

2. Ionization IONIZATION ENERGIES
Energy needed to liberate electron from that level.
GROUND STATE Lowest possible energy state for an electron in an atom.

3. Use the energy level diagram
Example #1
A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron.
What minimum energy did this photon have?
Try it!
Use the energy level diagram

4. So the photon had to provide to ionize/liberate the electron
Example #1
A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron.
What minimum energy did this photon have?
Free/liberated electron energy
So the photon had to provide
13.6 eV
to ionize/liberate the electron
Ground state energy (in eV)

5. Example #1
A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron.
What is the frequency of the photon that could provide this energy?
We have energy and need to find frequency…
We can use our equation E=hf!!
BUT… our energy is in eV, not joules
First convert the ionization energy
from eV into J

6. Example #1
A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron.
What is the frequency of the photon that could provide this energy?
Conversion table!

7. Example #1
A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron.
What is the frequency of the photon that could provide this energy?
Value to convert
Conversion factor (p.1 of Ref table)
1 eV = 1.6 x J
1 eV
1.6 x J
13.6 eV

8. Example #1
A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron.
What is the frequency of the photon that could provide this energy?
Value to convert
Conversion factor (p.1 of Ref table)
1 eV = 1.6 x J
1 eV
1.6 x J
13.6 eV
= 2.18 x J

9. Example #1
A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron.
What is the frequency of the photon that could provide this energy?
Now that we have energy of the photon in Joules, we can use an equation to solve for the frequency of this photon
(Yesterday’s lesson!)

10. Example #1
A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron.
What is the frequency of the photon that could provide this energy?
Ephoton =
2.18 x J
f = ?
h = 6.63 x J·s
Ephoton = hf = hc/λ
Ephoton = hf
f = (2.18 x J )/
(6.63 x J·s)
f = 3.29 x 1015 Hz

11. Back to our old friend, the energy level diagram for hydrogen…
Example #2
What happens to an electron in the n = 2 state of a hydrogen atom if it is hit by a 5.4 electron-volt photon?
Back to our old friend, the energy level diagram for hydrogen…

12. Energy for this electron =
Example #2
What happens to an electron in the n = 2 state of a hydrogen atom if it is hit by a 5.4 electron-volt photon?
State of n=2
Energy for this electron =
-3.4 eV

13. Example #2
What happens to an electron in the n = 2 state of a hydrogen atom if it is hit by a 5.4 electron-volt photon?
Hype!!!
Photon with 5.4 eV of energy
The electron GAINS this energy and gets hype

14. Electron be like “peace, I’m out” with 2.0 eV of energy in it’s pocket
Example #2
What happens to an electron in the n = 2 state of a hydrogen atom if it is hit by a 5.4 electron-volt photon?
If the electron initially has -3.4 eV and gains 5.4 eV from the photon…
- 3.4 eV eV = + 2 eV
Electron be like “peace, I’m out” with 2.0 eV of energy in it’s pocket
More scientifically… The electron will leave the atom with a kinetic energy of 2.0 eV.

15. Level Jumps
Initial Energy level of Electron
Initial Energy level of Electron
Equation
Energy of photon absorbed/emitted
An electron will jump to a higher level if the ABSORBED photon has exactly the right energy.
When an electron drops to a lower level a photon is EMITTED

16. Absorbing Photons Hype!!! Photon
Let’s say my dude Ellie the electron is chillin in energy level n = 3.
Then, Princess the photon rolls by and says “what’s up boiii”
Ellie the electron absorbs princess (electrons are selfish)
Ellie gets hype and gains energy!
Ellie could hop to higher energy levels OR get ionized.

17. Emitting Photons
Let’s say my dude Ellie the electron is chillin in energy level n = 5. He’s pretty hype
Photon
However, his girl Princess the photon decides to leave him.
At the same instant, he gets sad, looses energy, and drops down to a lower energy level

18. Example #3
What energy is needed to move an electron from the ground state of a hydrogen atom to its n = 4 level?
TRY IT

19. Example #3 Ephoton = Ei – Ef Ephoton = -13.6 eV – -0.85 eV
What energy is needed to move an electron from the ground state of a hydrogen atom to its n = 4 level?
Ephoton = Ei – Ef
Ephoton = eV – eV
Ephoton = eV Ef Ei

20. Example #4
An electron drops from the n = 4 level to the n = 3 level of a hydrogen atom.
What is the energy of the emitted photon?
Ephoton = Ei – Ef
Ephoton = eV – eV
Ephoton = eV Ei Ef

21. Example #4
An electron drops from the n = 4 level to the n = 3 level of a hydrogen atom.
What is the frequency of this photon?

22. Example #4
An electron drops from the n = 4 level to the n = 3 level of a hydrogen atom.
What is the frequency of this photon?
Ephoton =
1.056 x J
f = ?
h = 6.63 x J·s
Ephoton = hf = hc/λ
Ephoton = hf
f = (1.056 x J )/
(6.63 x J·s)
f = 1.6 x 1014 Hz

23. Example #5
When electrons drop from one energy level to another they can follow any path to the lower state. Each downward step produces a photon with a different energy.
How many different photons could be produced in a transition from the n = 4 level of hydrogen to the n = 1 level?
How many different photons could be produced in a transition from the d-level to the b-level of a mercury atom?
n =4
n = 3
n = 2
n = 1
6 possible photons d c b
3 possible photons

24. Absorption/Emission Spectrum
An EMISSION SPECTRUM is a pattern of bright lines on a dark background.
Analyze glow of a heated sample
An ABSORPTION SPECTRUM is a pattern of dark bands on a continuous spectrum.
Pass white light through a cold sample.

25. Absorption/Emission Spectrum
The existence of spectrums demonstrates that:
Energy in atoms is QUANATIZED – comes in discrete jumps.
Atoms can produce only specific sets of PHOTONS.

26. End of 6.1.2