# List 4 differences between electronic excitation and ionization of atoms?

Jun 25, 2017

Why four?

${\text{A" stackrel(Delta" ")(->) "A}}^{+} + {e}^{-}$ $\Leftarrow$ ionization

$\text{A" stackrel(hnu" ")(->) "A"^"*}$ $\Leftarrow$ excitation

1. Although the sign of the energy involved is the same $\left(+\right)$, usually the amount of energy involved differs (if not, it is a coincidence).
For example, the hydrogen atom has a first ionization energy of about $\text{13.61 eV}$, but its first excitation energy is about $\text{10.20 eV}$.
2. The final state of the electron differs. Ionizations leave the electron ejected from the atom. Excitations allow the electron to remain in the atomic region, and eventually the electron will relax down.
3. Excitations lead to electronic relaxation eventually, which releases photon(s). Ionizations don't allow emission of light, because the electron is no longer in that atom. Electronic relaxation:

4. There are selection rules for excitations, but not for ionizations. i.e. there are restrictions to how the electron can be excited (into what orbitals); there are no such rules for ionizations---just shine a laser with the right energy, and eject the electron.