1. Shielding and Photoelectron Spectroscopy

2. Multi-electron Atoms In atoms with multiple electrons there are two forces in play - attraction between electron and nucleus - repulsion between the multiple electrons Outer shell valence electrons feel repulsion of inner shell electrons, this reduces the net attraction they feel from the nucleus

3. Shielding or Screening The decrease in nuclear charge felt due to inner shell electrons “blocking” the full nuclear charge

4. Effective Nuclear Charge Way of describing the charge that outer valence electrons actually experience Effective nuclear charge = atomic number minus number of inner shell electrons

5. Result Outer valence electrons do not experience the same full nuclear charge as inner shell electrons According to coulomb’s law q 2 is smaller, therefore the energy holding the outer electrons in place is not as great

6. Photoelectron Spectroscopy Technique used to gather information about electrons in an atom Bombards atom with photons If photons are of sufficient energy, electrons will be emitted from the atom The energy the holds the electron on the atom can be determined by looking at the energy of the photon that causes emission

7. Data Photoelectron Spectroscopy Shows the amount of energy (in MJ) needed to remove the given number of electrons

8. Practice Looking at the PES for Si, sketch the graph for P Ar Ca

9. PES Data Energy (MJ) Which element (X or Y) is sodium and which is sulfur? How can you tell? Element X1046.843.670.50 Y23922.716.52.051.00