Summary:
- Electrons have a unique set of identifiers in the quantum numbers that describe their location and spin.
- The Pauli exclusion principle states that no two electrons in an atom can have the same set of four quantum numbers.
- If those three numbers are identical for two electrons, the spin numbers must be different in order for the two electrons to be differentiated from one another.
- The two values of the spin quantum number allow each orbital to hold two electrons.
- The figure below shows how the electrons are indicated in a diagram.