**Magnetic Quantum Number (m):**

This quantum number describes the behaviour of the electron in magnetic fields. We know that the movement of electrical charge is always associated with magnetic fields. Since the revolving electron possess angular momentum, it will give rise to a very small magnetic field which will interact with the external magnetic field of the earth. Under the influence of the external magnetic field, the electrons in given subshell orient themselves in certain preferred regions of space around the nucleus These are called to orbitals thus; this quantum gives the number of orbital in a given subshell. It is designed by m. The allowed values of m depend upon the value of *l*. For a given value of *l*, m can have, values – *l* through 0 to + *l*, that is m = – *l*,…. 0, ….. + *l*

In other words, there are (2 *l* + 1) values of m for each value of *l*. For example, if *l* = 0, m has only one value, i.e. m = 0

i.e. s sub-shell has only one orbital called s—orbital

If *l* =1,m may be, – 1, 0, + 1

These are designated by alphabetic subscripts ( Px, Py and Pz)