The energy levels
in atoms and ions are the key to the production and detection of light. Energy
levels or "shells"exist for electrons in atoms and molecules. The
colors of dyes and other compounds results from electron jumps between these
shells or levels. The colors of fireworks result from jumps of electrons from
one shell to another. Observations of light emitted by the elements is also
evidence for the existence of shells, subshsells and energy levels. The kinds
of light that interact with atoms indicate the energy differences between
shells and energy levels in the quantum theory model of the atom. Typically the
valence electrons are the ones involved in these jumps.
Atoms have two
kinds of states; a ground state and an excited state. The ground state is the
state in which the electrons in the atom are in their lowest energy levels
possible (atoms naturally are in the ground state). This means the electrons
have the lowest possible values for "n" the principal quantum number.
Specific quantized amounts of energy
are needed to excite an electron in an atom and produce an excited state. The
animation shows the opposite of excitation. It shows how the excited hydrogen
atom with an electron in the n = 3 shell can release energy. If the electron in
hydrogen only drops to the n = 2 shell the energy matches a pulse of red light.
Note the size of the electron cloud in
the excited atom changes when the electron moves from shell to shell. The size
of the atom decreases in volume when the electron goes from the n=3 shell to
the n = 2 shell. On average the electrons are closer to the nucleus for lower
values of "n". The electron cloud is related to the most probable
distance between the nucleus and the electron. The most probable distance
increases with increasing "n" value. The excited electron is still
"in" the atom even in an excited state. The valence electron will
only escape the atom if the electron is given an amount of energy equal to the
ionization energy for that atom