Principal quantum number

The Principal quantum number is the main quantum number of an atomic orbital. It is usually written by the letter n. It can have values 1, 2, ...

• The atomic orbitals with n=1 are said to be in the 'K'-shell
• The atomic orbitals with n=2 are said to be in the 'L'-shell
• The atomic orbitals with n=3 are said to be in the 'M'-shell
• The atomic orbitals with n=4 are said to be in the 'N'-shell