Atomic Orbital: A mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom.
Quantum Mechanics: The branch of physics dealing with atomic and subatomic systems which provides a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter.
Valence Electrons:The electrons in an atom's outermost orbitals; these are involved in forming bonds with other atoms.