Quantum numbers: There are a set of four quantum numbers which specify the energy, size, shape and orientation of an orbital. To specify an orbital only three quantum numbers are required while to specify an electron all four quantum numbers are required.
(i) Principal quantum number (n):It identifies shell, determines sizes and energy of orbitals
Electron Configuration Table
| N | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
| Shell No. | K | L | M | N |
| Total number of orbitals in a shell = n2 | 1 | 4 | 9 | 16 |
| Maximum number of electrons = 2n2 | 2 | 8 | 18 | 32 |
Azimuthal quantum number (l): Azimuthal quantum number. ‘l’ is also known as orbital angular momentum or subsidiary quantum number. l. It identifies sub-shell, determines the shape of orbitals, energy of orbitals in multi-electron atoms along with principal quantum number and orbital angular momentum, i.e., 
Subshell Notation Table
| Subshell notation | s | p | d | f | g |
|---|---|---|---|---|---|
| Value of ‘l’ | 0 | 1 | 2 | 3 | 4 |
| Number of orbitals | 1 | 3 | 5 | 7 | 9 |
Magnetic quantum number or Magnetic orbital quantum number (ml):
Itgives information about the spatial orientation of the orbital with respect tostandard set of co-ordinate axis.For any sub-shell (defined by ‘l’ value) 2l+1 values of ml are possible.For each value of l, ml = – l, – (l –1), – (l–2)… 0,1… (l – 2), (l–1), l
Electron spin quantum number (ms): It refers to orientation of the spin of the electron. It can have two values +1/2 and -1/2. +1/2 identifies the clockwise spin and -1/2 identifies the anti- clockwise spin.