1. Write the electron configurations for
Oxide
Germanium
Chromium(III)

2. Wave Reminder Wave-particle duality Photon – particle of light
Every photon has a wavelength, frequency, energy
Know one, can calculate the other two

3. Photoelectron Spectroscopy (PES)
***Key point for today: PES provides evidence for the shell model of the atom***

4. Photoelectric Effect Simulation

6. PHET simulation: http://phet.colorado.edu/en/simulation/photoelectric
Einstein won the Nobel prize in Physics in 1921 for his explanation of the photoelectric effect (not for his theory of relativity)

7. Key Points to Photoelectric Effect
Light with higher energy (higher frequency) is able to ionize atoms (remove electrons)
“Before Einstein's explanation, the photoelectric effect was a real mystery. Scientists couldn't really understand why low-frequency high-intensity light (lots of red light) would not cause electrons to be emitted, while higher-frequency low-intensity light (a faint amount of violet) would. Knowing that light is made up of photons, it's easy to explain now. It's not the total amount of energy (i.e., the intensity) that's important, but the energy per photon.”

8. Photoelectron Spectroscopy
PES apparatus:
iramis.cea.fr

9. PES Data Electrons generally farther from the nucleus Electrons
generally closer to the nucleus
Each peak represents the electrons in a single sublevel in the atom
The bigger the peak – the more electrons
Number of electrons
Energy to remove an electron
(binding energy)
(increases to the left!) 

10. Hydrogen vs. Helium Helium Hydrogen #e- #e-  energy  energy
1 electron in 1s
2 electrons in 1s
The helium peak is twice as tall because there are twice as many electrons in the 1s sublevel

11. Hydrogen vs. Helium Helium Hydrogen #e- #e-  energy  energy
1 electron in 1s
2 electrons in 1s
The helium peak is farther to the left (higher energy) thus more energy is needed to remove
the 1s electrons in helium. They must be held more tightly because there is a higher effective
nuclear charge. (Helium has 2 protons pulling on 1s but hydrogen only has 1)

12. Oxygen (1s22s22p4) Number of electrons 2 electrons in 2s
4 electrons in 2p
Energy to remove an electron
(binding energy)
(increases to the left!) 

13. Key Points to Reading a PES
Size of peaks indicates # of electrons
Go in energy level or shell order (all the 3rd energy level data is together)
Sometimes 1s is omitted because it’s so high in energy that it’s off the graph

14. Scandium (1s22s22p63s23p64s23d1) Number of electrons
*Notice that it takes more
energy to remove an electron from
3d than from 4s.
This is because as electrons are
added to 3d they shield 4s thus it’s
easier (takes less energy) to remove
4s electrons compared to 3d
electrons.
Remember when transition metals make
positive ions - it’s the s electrons that are
lost first!
2 in1s
2 in 3s
2 in 4s
1 in 3d
2 in 2s
6 in 2p
6 in 3p
Energy to remove an electron
(binding energy)
(increases to the left!) 

15. Example 1: Number of electrons Identify the element whose
PES data is shown to the right.
Sodium
Why is one peak much larger
Than the others?
This peak represents 6 electrons
In the 2p sublevel the other
Peaks represent only 1 or 2
electrons
In which sublevel are the electrons
Represented by peak A 3s A
Energy 

16. Example 2: Oxygen Nitrogen #e- #e-  energy  energy
The PES data above shows only the peak for the 1s electrons. Why is the peak for
Oxygen farther to the left?
It takes less energy to remove a 1s electron from nitrogen because it has a lower
Effective nuclear charge (less protons) than oxygen

17. Example 3: Number of electrons Draw the expected PES
Spectrum for the element boron
Energy 

18. What ion could this data represent? Explain.

19. Identify all of the peaks in the PES below. What is missing
Identify all of the peaks in the PES below. What is missing? What neutral element is this data from?

20. Write an electron configuration and draw a photoelectron spectra for aluminum.
Circle the peak that would change if this atom were ionized.