e-e- Ground state

Excited state

Electrons can only be atspecific energy levels,NOT between levels.

Color = Energy of Photons

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 329

Energy Level

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 329

A

B

C

D

Ground state

Ener

gy

Fourexcitedstates

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

Excitation of Hydrogen Atoms

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 328

Return to Ground State

Frequency A

Frequency B

Frequency C

n = 2

n = 1

n = 3

A

B

C

A + B = C

Bohr Model of the Atom

Electrons in Atomsnucleus (+)

electron (-)

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

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

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

Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

(a) Electronic absorption transition

(b) H2 emission spectrum (top), H2

absorption spectrum (bottom)

Bohr’s Model

Nucleus

Electron

Orbit

Energy Levels

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-

e-

e-

e-

e-

e-

e-

e-

e-

e-

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

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

Modern View

• The atom is mostly empty space• Two regions– Nucleus

• protons and neutrons– Electron cloud

• region where you might find an electron