# What is quantum number?

## What is a quantum number?

A quantum number is a number that describes the state of a quantum system. In the context of atoms, quantum numbers are used to describe the energy, angular momentum, and spin of electrons.

There are four quantum numbers that are used to describe electrons:

• Principal quantum number (n): This quantum number describes the energy level of the electron. The possible values of n are integers 1, 2, 3, 4, etc.

• Azimuthal quantum number (l): This quantum number describes the shape of the orbital that the electron is in. The possible values of l are integers 0 to n-1.

• Magnetic quantum number (m): This quantum number describes the orientation of the orbital in space. The possible values of ml are integers from -l to l, inclusive.

#### Spin quantum number (s): This quantum number describes the spin of the electron. The possible values of ms are +1/2 and -1/2.

The four quantum numbers together uniquely identify the state of an electron in an atom.

For example, the electron in the ground state of hydrogen has the quantum numbers n = 1, l = 0, m = 0, and s = -1/2.

Quantum numbers are important in understanding the behavior of electrons in atoms. They can be used to calculate the energy of electrons, the probability of finding an electron in a certain region of space, and the interactions between electrons.

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