1. ELECTRON CONFIGURATIONS
The arrangement of electrons in an atom

2. Part I: RULES FOR E- CONFIGURATIONS
1. The Aufbau Principle
Each electron occupies the lowest energy orbital available
Follow the aufbau diagram for the sequence of atomic orbitals

3. 2. Pauli Exclusion Principle
Electrons are able to spin in only two directions
Only two electrons may occupy a single orbital
Elecrons in the same orbital must have opposite spins

4. 3. Hund’s Rule
Electrons fill empty orbitals in a sublevel first BEFORE sharing an orbital
Why? Because negatively charged electrons want to be as far away from each other as possible 2p

5. Part II: ORBITAL DIAGRAMS
Represent an atom’s electron configuration
A line = each orbital
Practice: Li, N, Ne 1s 2s 2p C

6. Part III: ELECTRON CONFIGURATIONS
Superscripts = number of electrons in the orbital
Add up superscripts = should equal total # of electrons in atom
Practice: Ca, N, Ga

7. Part IV: NOBLE GAS NOTATION
Electron configuration can be represented using the noble gas notation for the noble gas in the previous period and the electron configuration for the energy level being filled
Practice: P, Ca, Sr