The electron can have only one value of n at a given time. A ground state H atom can be promoted to an excited state by absorption of light of appropriate frequency, or by molecular collisions between atoms in the gas phase. On this diagram we have given orbital designations such as 1s, 2s, etc. We make one final comment before we leave our discussion of energy of the H atom. We have not made a distinction between total energy E and orbital energy in this discussion.
Chemists often label orbital energies with the lower case Greek letter epsilon, .
For the H atom there is no distinction between E and . However, be forewarned that for multielectron atoms it will be important to make such a distinction. The only variable in this equation is r, the distance between the electron and the proton. Since in atomic units the value of a 0 is 1, we normally do not explicitly exhibit it in the equation. Chemists usually refer to the wave function of the H atom as the atomic orbital of the atom.