The Aufbau Principle and Hund's Rule are two fundamental concepts in understanding the arrangement of electrons in orbitals.

The Aufbau Principle states that electrons fill the lowest energy levels available before occupying higher energy levels. In other words, electrons are added to orbitals in a systematic way based on increasing energy level. For example, in the electron configuration of nitrogen (N) (1s² 2s² 2p³), the 1s orbital is filled first, followed by the 2s orbital, and finally, the 2p orbital.

Hund's Rule, on the other hand, states that when orbitals of equal energy (degenerate orbitals) are available, electrons will occupy separate orbitals within the same energy level before pairing up. This is known as the 'bus seat rule.' For instance, in the electron configuration of carbon (C) (1s² 2s² 2p²), each of the 2p orbitals is singly occupied before any two electrons occupy the same orbital.

These principles provide a guideline for the filling of electron orbitals in atoms, ensuring the stability and organization of electron configurations. They help establish the distinct arrangements seen in the periodic table, allowing for the prediction of chemical properties and reactivity based on electron configurations.