1. Atomic Structure
Orbital Diagrams

2. Aufbau principle
Electrons are added one at a time to the lowest energy orbitals available until all the electrons in an atom have been accounted for fully.

3. Pauli exclusion principle
An orbital can hold a maximum of two electrons. In order for two electrons to occupy the same orbital, they must spin opposite one another. These electrons are said to be “paired”. Single electrons are “unpaired”.

4. Hund’s rule
Electrons occupy equal-energy orbitals so that a maximum number of unpaired electrons results. This is due to the charges on the electrons causing them to repel one another.

5. Maximum Number of Electrons in each Sublevel
Number of Orbitals
Max # of Electrons s 1 2 p 3 6 d 5 10 f 7 14

6. Diagonal Rule for Electrons

7. The elements in these regions of the Periodic Table end within these sublevels.