The energy corresponding to the quantum state n is given
is another collection of physical constants, which for hydrogen
has a value of 313 kcal .
The allowed energy levels for hydrogen are diagramed at the right.
By convention, energy is expressed relative to that of an ionized
atom, with the electron at rest but infinitely far away. The energy
of any atom with its electron still bound to it must be less than
zero, or negative. Positive energy refers to the kinetic energy
that the removed electron has, if it is not at rest.