UV/VIS SPECTRA FOR ATOMS
The energy of ultraviolet and visible electromagnetic radiation is sufficient to cause a change in an atom’s valence electron configuration. Sodium, for example, has a single valence electron in its 3s atomic orbital.
As shown in Figure 10.19, unoccupied, higher energy atomic orbitals also exist.
Absorption of a photon is accompanied by the excitation of an electron from a lower-energy atomic orbital to an orbital of higher energy.
Not all possible transitions between atomic orbitals are allowed.
For sodium the only allowed transitions are those in which there is a change of ±1 in the orbital quantum number (l); thus transitions from s é p orbitals are allowed, and transitions from s é d orbitals are forbidden.