Question

What quantum numbers are needed to specify a hydrogenic atomic orbital?

Answer 1

You need three quantum numbers, `n, l` and `m_l` to completely specify an orbital.

Explanation:

The principal quantum number, `n`, specifies the energy and the relative size of the orbital.

The azimuthal quantum number, `l`, specifies the shape of the orbital.

The magnetic quantum number, `m_l`, specifies the orientation of the orbital in space.

For example, each of the three 2p orbitals has a different set of `n, l` and `m_l`.