Quantum Numbers

The term quantum number is used to identify the various energy levels available with the atom in which the electron of the atom can reside. The word quantum is used to signify that all the energy levels which are avail ables to an electron are governed by the laws of quantum mechanics.

Just as college student is identified by (1) his name (2) the name of his college (3) class in he is studying and (4) the locality in which his college is situated, an electron in an atom is completely described by its four quantum numbers. Thus the quantum numbers serve as identification numbers or labels which completely define the electron in an atom i.e. these numbers-

1. Specify the position (or)location of an electron in an atom.
2. Predict the direction of spin or self rotation of the electron.
3. Determine the energy and angular momentum of the electron.

Four quantum numbers which are required to completely specify the character of an electron in an atom.

1. Principle quantum number (n)
2. Azimuthal quantum number (l)
3. Magnetic quantum number (m)
4. Spin quantum number (s)

Each quantum number refers to a particular character of an electron in an atom.