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A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron. –What minimum energy did this photon have? Example # eV
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6.1.2 Energy Levels
Photons in / Photons out
Ionization
IONIZATION ENERGIES
Energy needed to liberate
electron from that level.
GROUND STATE Lowest possible
energy state for an electron in an
atom.
• A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron.– What minimum energy did this photon have?
Example #1
13.6 eV
• A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron.– What is the frequency of the photon that could
provide this energy?
Example #1
2.176 x 10-18 J
eVJx
eVxJ
1106.1
6.13
19
• A photon strikes an electron in the ground state of a hydrogen atom, liberating the electron.– What is the frequency of the photon that could
provide this energy?
Example #1
Ephoton = hf
2.176 x 10-18 J = (6.63 x 10-34 J·s) f
f = 3.3 x 1015 Hz
• What happens to an electron in the n = 2 state of a hydrogen atom if it is hit by a 5.4 electron-volt photon?
Example #2
The electron will leave the atom with a kinetic energy of 2.0 eV.
Level Jumps
• An electron will jump to a higher level if the ABSORBED photon has exactly the right energy.
• When an electron drops to a lower level a photon is EMITTED
fiphoton EEE
Equation
• What energy is needed to move an electron from the ground state of a hydrogen atom to its n = 4 level?
Example #3
Ephoton = Ei – Ef
Ephoton = -13.6 eV – -0.85 eV
Ephoton = -12.75 eV
• An electron drops from the n = 4 level to the n = 3 level of a hydrogen atom.– What is the energy of the emitted photon?
Example #4
Ephoton = Ei – Ef
Ephoton = -0.85 eV – -1.51 eV
Ephoton = +0.66 eV
• An electron drops from the n = 4 level to the n = 3 level of a hydrogen atom.– What is the frequency of this photon?
Example #4
Ephoton = hf
1.056 x 10-19 J = (6.63 x 10-34 J·s) f
f =1.6 x 1014 Hz
• When electrons drop from one energy level to another they can follow any path to the lower state. Each downward step produces a photon with a different energy.– How many different photons could be produced in a transition
from the n = 4 level of hydrogen to the n = 1 level?
– How many different photons could be produced in a transition from the d-level to the b-level of a mercury atom?
Example #5
6 possible photons
d
c
b 3 possible photons
n =4
n = 3
n = 2
n = 1
Absorption/Emission Spectrum• An EMISSION SPECTRUM is a pattern of bright lines on a
dark background.– Analyze glow of a heated sample
• An ABSORPTION SPECTRUM is a pattern of dark bands on a continuous spectrum.– Pass white light through a cold sample.
Absorption/Emission Spectrum• The existence of spectrums demonstrates that:
– Energy in atoms is QUANATIZED – comes in discrete jumps.
– Atoms can produce only specific sets of PHOTONS.
End of 6.1.2