Editing Quantum number (section)

{{Short description|Notation for conserved quantities in physics and chemistry}}
{{Redirect|Q-number|the Q-theory concept|Q-analog|the number format|Q (number format)}}
[[Image:Atomic orbitals n123 m-eigenstates.png|thumb|Single electron orbitals for hydrogen-like atoms with quantum numbers {{math|1=''n'' = 1, 2, 3}} (blocks), {{mvar|{{ell}}}} (rows) and {{mvar|m}} (columns). The spin {{mvar|s}} is not visible, because it has no spatial dependence.]]
{{Quantum mechanics|fundamentals}}
In [[Quantum mechanics|quantum physics]] and [[chemistry]], '''quantum numbers''' are quantities that characterize the possible states of the system. 
To fully specify the state of the electron in a hydrogen atom, four quantum numbers are needed. The traditional set of quantum numbers includes the [[Principal quantum number|principal]], [[Azimuthal quantum number|azimuthal]], [[Magnetic quantum number|magnetic]], and [[Spin quantum number|spin]] quantum numbers. To describe other systems, different quantum numbers are required. For subatomic particles, one needs to introduce new quantum numbers, such as the [[flavour (particle physics)|flavour]] of [[quarks]], which have no classical correspondence.

Quantum numbers are closely related to [[eigenvalues]] of [[observable]]s. When the corresponding observable commutes with the [[Hamiltonian (quantum mechanics)|Hamiltonian]] of the system, the quantum number is said to be "[[Good quantum number|good]]", and acts as a [[constant of motion]] in the quantum dynamics.