Quantum number
A quantum number is a number used to parametrise certain properties of particless or other systems in quantum mechanics. Combinations of quantum numbers can be used to identify eigenstates of the system.Each quantum number represents a specific degree of freedom that any particle can occupy. In this viewpoint, they can be seen as analogous to properties in classical systems. For example, the principal quantum number of an electron in an atom is roughly analogous to its orbital distance in classical mechanics. However, the defining characteristic of quantum mechanics is that these are quantised: that is, there is a specific discrete set of values that are allowed for each quantum number. This quantization property is the source of the word "quantum" in "quantum mechanics".
The nature of the sets of allowed values is quite fundamental. In the case of electrons in an atom, the restrictions on the allowed values of l and ml arise from the nature of the boundary condition imposed by the shape of the potential generated by the nucleus, and the restriction on ms is due to the electron itself.
Examples include:
- Quantum numbers of elementary particles:
- Particle spinss
- Baryon number
- Lepton number
- Electric charge
- Color charge
- Isospin
- Parity
- Charge conjugation
- Quantum numbers of electron orbitalss in atoms:
- the Principal quantum number, n = 1, 2, 3, ...
- the Azimuthal quantum number, l = 0, 1, ..., n-1 (also known as the angular quantum number)
- the Magnetic quantum number, ml = 0, ñ1, ñ2,..., ñl
- the Spin quantum number, ms = -1/2, 1/2 (these are the possible particle spinss of an electron)
- Quark quantum numbers:
- Strangeness
- Charm
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