E-e- e-e- Ground state Excited state Electrons can only be at specific energy levels, NOT between...
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Transcript of E-e- e-e- Ground state Excited state Electrons can only be at specific energy levels, NOT between...
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e-e- Ground state
Excited state
Electrons can only be atspecific energy levels,NOT between levels.
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Color = Energy of Photons
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 329
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Energy Level
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 329
A
B
C
D
Ground state
Ener
gy
Fourexcitedstates
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An Excited Lithium Atom
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 326
Photon ofred lightemitted
Li atom inlower energy state
Excited Li atom
Ener
gy
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Excitation of Hydrogen Atoms
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 328
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Return to Ground State
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Frequency A
Frequency B
Frequency C
n = 2
n = 1
n = 3
A
B
C
A + B = C
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Bohr Model of the Atom
Electrons in Atomsnucleus (+)
electron (-)
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
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Bohr Model
• electrons exist only in orbits with specific amounts of energy called energy levels
• Therefore…• electrons can only gain or lose certain
amounts of energy• only certain photons are produced
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
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Bohr Model
1
23
456 • Energy of photon
depends on the difference in energy levels
• Bohr’s calculated energies matched the IR, visible, and UV lines for the H atomCourtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
nucleus
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Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.
(a) Electronic absorption transition
(b) H2 emission spectrum (top), H2
absorption spectrum (bottom)
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Bohr’s Model
Nucleus
Electron
Orbit
Energy Levels
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Bohr Model of Atom
The Bohr model of the atom, like many ideas in the history of science, was at first prompted by and later partially disproved by experimentation.
http://en.wikipedia.org/wiki/Category:Chemistry
Increasing energyof orbits
n = 1
n = 2
n = 3
A photon is emittedwith energy E = hf
e-e-
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An unsatisfactory model for the hydrogen atom
According to classical physics, lightshould be emitted as the electron circles the nucleus. A loss of energywould cause the electron to be drawncloser to the nucleus and eventuallyspiral into it.
Hill, Petrucci, General Chemistry An Integrated Approach 2nd Edition, page 294
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Quantum Mechanical Model
Modern atomic theory describes the electronic structure of the atom as the probability of finding electrons within certain regions of space (orbitals).
Niels Bohr &Albert Einstein
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Modern View
• The atom is mostly empty space• Two regions– Nucleus
• protons and neutrons– Electron cloud
• region where you might find an electron