1. Electron Configuration
If e- prefer to be near the nucleus, then they will fill orbitals from nucleus out
Remember Aufbau?
Fill orbitals in order of increasing energy
Low n to high n, s before p before d before f
Must also consider Pauli Exclusion Principle and Hund’s Rule

5. Can you explain why orbital energy increases with increasing n?
Hint: Coulomb’s Law and 2
What about s < p < d < f?
Must consider shielding and penetration

6. Do all e- feel same pull/attraction from/to nucleus? Why or why not?
Besides distance, must also consider shielding or screening

7. Zeff
Core electrons shield or screen valence electrons from the charge of the nucleus
Nuclear charge is not experienced the same by all electrons.
Outer electrons experience it less, so Z is reduced. The new Z is called Zeff
Zeff = Z – S
where Z is actual nuclear charge (#p in nucleus) and S is shielding constant (# core e-)

8. How many protons and electrons? Can you write the e- configuration?
Consider Li.
How many protons and electrons?
Can you write the e- configuration?
Do the electrons in ring 1 feel same pull as the electron in ring 2?
What charge do the ring 1 e’s feel?
What charge does the ring 2 e- fell?
What if the e- in the second ring could penetrate the first ring? Would the charge it feels change?

9. Penetration
Space in the square: an electron from 2s penetrating ring 1
Space in the oval: an electron from 2p penetrating ring 1
There is less penetration for 2p so it becomes higher in energy than 2s because more shielding, less Coulombic attraction
This explains Aufbau’s Building Up Principle and electron configurations

11. In 1905, Einstein explained the photoelectric effect
If you shine light on a clean metal surface, e- can be emitted (as color or light)
To eject an e-, the light hitting the sample must have a minimum energy (threshold energy)
If not at threshold energy, no light will be emitted from sample (no matter the intensity or amount of light)
Einstein assumed that the radiant energy hitting the surface was quantized and has
Ephoton = h

12. PES: Photoelectron Spectroscopy
PES measures the amount of energy needed to eject electrons
The energy gives a sense of the binding energies of electrons in a substance.
Electron binding energy is a measure of the energy required to free electrons from their atomic orbits (ionization energy)
as increase E, harder to remove, so probably closer to the nucleus for ex

13. PES: Photoelectron Spectroscopy
The binding energies of the measured electrons are characteristic of the chemical structure and molecular bonding of the material
One of the most sensitive and accurate techniques for measuring the energies and shapes of electronic states and molecular and atomic orbitals
Provides direct evidence for the shell model

16. PES

17. Give e- configuration and identify the element