1. Electron Configuration

2. Order of Energy Levels
Inner shell electrons “shield” outer electrons from the full positive effect of the nucleus – “screening effect”
Different orbitals shield the outer electrons more effectively than others
Not all orbitals experience the same + charge from the nucleus
Therefore different orbitals have different potential energies

4. Degenerate Orbitals
Orbitals that have the same energies

5. Electron Spin Electron behaves as if it is spinning on its axis
Fourth Quantum number (ms) is the spin number
It can be either –1/2 or +1/2

6. Spinning electrons produce magnetic fields

7. Pauli Exclusion Principle
No two electrons can have the same set of four quantum numbers (n, l, ml, ms)
If an orbital has two electrons in it, they must have different spins
Electrons in the same orbital with different spins are called paired electrons

8. Configuration Arrangement of electrons in the atom
Aufbau Principle – orbitals fill in order of increasing energy

9. Orbital Diagram of Li ( 3 e-)
1s22s1

10. Orbital Diagram of B (5 e-)
1s22s22p1

11. Hund’s Rule
Electrons occupy degenerate orbits singly first

12. Orbital Diagram of C (6 e-)
1s22s22p2

13. Orbital Diagram of Ne (10 e-)
Configuration 1s22s22p6

14. Valence Electrons Outer shell electrons
Ones in the last main energy level
▪ K 1s22s22p63s23p64s valence e
Fe 1s22s22p63s23p64s23d valence e