# CBSE Class 9 Answered

**Neil Bour's explain all the quantum number in his model.explain**

**Principal quantum number ( n):**

Has positive values of 1, 2, 3, etc.

As *n* increases, the orbital becomes larger and this means that the electron has a higher energy level and is less tightly bound to the nucleus.

**Azimuthal quantum number ( l ):**

Has values from 0 to *n* – 1.

This defines the shape of the orbital, and the value of *l* is designated by the letters *s*, *p*, *d*, and *f*, which correspond to values for *l* of 0, 1, 2, and 3.

In other words, if the value of *l* is 0, it is expressed as *s*; if *l* = 1 = *p*, *l *= 2 = *d*, and *l* = 3 = *f*.

**Magnetic quantum number ( m_{l}):**

Determines the orientation of the orbital in space relative to the other orbitals in the atom.

This quantum number has values from -*l* through 0 to +*l*.

**Spin quantum number ( m_{s}):**

Specifies the value for the spin and is either +1/2 or -1/2.

No more than two electrons can occupy any one orbital.

In order for two electrons to occupy the same orbital, they must have opposite spins