The Pauli exclusion principle

The Pauli exclusion principle states that no two electrons (or similar particles) within an atom can occupy the same quantum state simultaneously. In more understandable terms, each electron has its own unique set of properties, and they cannot be in the same place with the same energy and spin at the same time. This principle explains why electrons fill different energy levels around an nucleus, leading to the structure of atoms and the diversity of chemical elements. It essentially prevents electrons from stacking together in exactly the same way, maintaining order and stability in matter.