Structure Of Atom

The electron in a H atom's stationary state moves in a circle around the nucleus.

An atom can take only certain distinct energies $\mathrm{E}_1, \mathrm{E}_2, \mathrm{E}_3$, etc. These allowed states of constant energy are called the stationary states of atom.

An atom in a stationary state does not emit electromagnetic radiation as long as it stays in the same state.

When an electron makes a transition from a higher energy stationary state to a lower energy stationary state, then it emits a photon of light.