An atomic orbital is a region in an atom where there is a high probability of finding electrons. Atomic orbitals are defined by quantum numbers and have specific shapes and orientations.
Quantum Numbers: Set of four numbers that describe the unique quantum state of an electron in an atom: principal (n), azimuthal (l), magnetic (m_l), and spin (m_s).
Pauli Exclusion Principle: A rule stating that no two electrons in an atom can have identical sets of quantum numbers.
Aufbau Principle: \text{A guideline for electron configuration that states electrons fill lower-energy orbitals first before moving to higher-energy ones.}