*Hello friends welcome once again on our blog. In our last post we’ve discussed Larmor Precession . In this post we are going to discuss Space Quantisation of an atom, which is another important topic in Atomic Physics.*

In Bohr-Sommerfeld atomic model, the space around nucleus is quantised, i.e. the distribution

of electrons in these orbits is in accordance with quantum number.

**B**,the electron orbit precesses about the field direction as axis(Larmor Precession).

Fig 1. Vector L traces a cone around vector B. |

The electron orbital angular momentum vector **L **traces a cone around **B **such that angle ϴ between **L **and **B **remains constant as shown in figure.

**B**is along z-axis, the component of

**L**parallel to the field is :

According to the quantisation principle :

This angle ϴ between **L **and the z-axes is determined by the quantum number ‘l’ & ‘ml’.

In other words, the angular momentum vector **L **can have (2n+1) discrete orientations, with respect to the magnetic field.

The quantisation of the orientation of atom in space is known as space quantisation.

**L**corresponding to

*l=2*is shown in fig. below:

Fig 2.Space quantisation of vector L corresponding to L=2. |

For *l=2 *we have,

*ml = 2,1,0,-1,-2*

*Lz = 2h/2π ,h/2π, 0, -h/2π ,-2h/2π.*

**L**with respect to field

**B**are given by :

Note:- **L **can never be aligned exactly parallel or antiparallel to **B**, since |ml| is always smaller than √l(l+1).

*This is Space Quantisation. You can ask any question related to this post in comment section. *