1. Electrons can only be at specific energy levels, NOT between levels.
Excited state e- e-
Ground state

2. Color = Energy of Photons
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 329

3. Energy Level Four excited states Energy Ground state D C B A
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 329

4. An Excited Lithium Atom
Excited Li atom
Energy
Photon of
red light
emitted
Li atom in
lower energy state
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 326

5. An Excited Lithium Atom
Excited Li atom
Energy
Photon of
red light
emitted
Li atom in
lower energy state
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 326

6. Excitation of Hydrogen Atoms
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 328

7. Return to Ground State

8. Frequency A n = 3 Frequency B n = 2 Frequency C n = 1 A C B A + B = C
n = 1 corresponds to the orbit closest to the nucleus and is the lowest in energy.
A hydrogen atom in this orbit is called the ground state, the most stable arrangement for a hydrogen atom.
As n increases, the radii of the orbit increases and the energy of that orbit becomes less negative.
A hydrogen atom with an electron in an orbit with n >1 is in an excited state — energy is higher than the energy of the ground state.
Decay is when an atom in an excited state undergoes a transition to the ground state — loses energy by emitting a photon whose energy corresponds to the difference in energy between the two states.
The difference in energy ΔE between any two orbits or energy levels is ΔE = En1 – En2 , where n1 is the final orbit and n2 the initial orbit.
Substituting in Bohr’s equation gives
ΔE = – hc (1/n21 – 1/n22).
• Since ΔE = hc/, then 1/ = –(1/n21 – 1/n22).
• This is the same equation that Rydberg obtained experimentally except for the negative sign, which indicates that energy is released as the electron moves from orbit n2 to orbit n1 because orbit n2 is at a higher energy than orbit n1 . A C B
A + B = C