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Solid Sphere Model or
Billiard Ball Model
John Dalton
Plum Pudding Model
J.J. Thomson
Planetary Model or Nuclear Model
Ernest Rutherford
http://mhsweb.ci.manchester.ct.us/Library/webquests/atomicmodels.htm
• Rutherford’s model did not account for
chemical properties or actual arrangement
of the electrons around the nucleus
– The way subatomic particles arrange
themselves (mostly e-) affects properties of
atoms like chemical behavior
• To account for chemical behavior must look
at electron configuration
– Idea that came from studying behavior of light
and atoms and electromagnetic radiation
Flaws with Rutherford’s Model, ctd.
If an atom is mostly empty space, and if the electron is
floating around in that empty space, then the atom
should collapse (since the electron would be
attracted to the nucleus)
Niels Bohr proposes that
e- are in circular paths
around the nucleus
(orbits/energy levels)
Bohr Model or Orbit Model
Neils Bohr
• First we will look at properties of light and
waves
• Then we will look at the modifications to
Rutherford’s model of the atom
– Mainly Bohr and Quantum Mechanics
Electromagnetic Radiation
• A way that energy travels through space
– Ex. Sun, microwaves, x-rays, etc.
• Although the forms of E are different, they
have important similarities
– Wavelike behavior
– Travel at speed of light in vacuum
c= 3x108 m/s
(which is 186,000 miles/second)
Radiation moves like a wave

Waves characterized by two properties:
wavelength () and frequency ()
: distance between waves (crest to crest)
measured in length
units: usually nm (How does this relate to m?)
: number of waves passing through a fixed point
in one second
units: per second (1/s or s-1 or Hz)
How do  and  relate?
Suppose this is one secondwhat is happening?
Waves move at the speed of light, c
– Recall: wavelength and frequency are
inversely proportional
c =  = length/time (nm/s or m/s)
• What is the wavelength, in nm, of light with
a frequency of 3.91x1014 s-1?
• What is the frequency of light with a
wavelength of 456 nm?
• Do your answers make sense?
Continuum of waves: shows the different forms of
radiation and how they relate energetically
Comparing Energy
Compare the energy of radio waves (~100
m) to that of UV-rays (10-4 m)
What are these wavelengths in nm?
What are the frequencies of these
wavelengths?
What about Energy, E?
• Proposed by Max Planck in 1900
– Energy is quantized
– Comes in small, discrete, whole # packets
• E is proportional to frequency and inversely
proportional to wavelength:
E = nh = nhc/
h=Planck’s constant = 6.626x10-34 J·s
Quantized Energy
• Means energy comes in small whole #
packets of nh is the small whole # packet
of energy (n is a multiple integer)
• Can only travel in increments of say 1
mph, 2mph, 3mph (not 1.5 mph)
– More relevant for small objects like e– Less noticeable as object get bigger (like car
or a human)
• In 1905, Einstein used Planck’s theory to
explain the photoelectric effect.
– If you shine light on a clean metal surface,
electrons can be emitted (in the form of color
and light)
– Einstein assumed that the radiant energy
hitting metal surface behaves like a stream of
tiny energy packets (quanta)
– Einstein calls these streams of energy
photons
Ephoton = h
Meaning, radiant energy is quantized
Photoelectric Effect
• To eject an e-, the light hitting the sample must have
a minimum energy (threshold energy or work
function).
• If not at threshold energy, no light will be emitted
from sample.
– no matter the intensity or amount of light
– This is the photoelectric effect
Think about cathode ray, will it work with regular light
bulb as energy source (vs. cattle prod)?
• What is the energy of a photon whose  =
589 nm?
• What is the energy per mol of the photon?
Need NA
Dual Nature of Light
• Einstein believed that light was a stream of
photons (particles)
• Means there is a dual nature of light
– Has properties of both waves (move like
waves) and particles (has mass and energy is
quantized)
Flaws with Rutherford’s Model, ctd.
If an atom is mostly empty space, and if the electron is
floating around in that empty space, then the atom
should collapse (since the electron would be
attracted to the nucleus)
In 1913, Bohr proposes
that e- are in circular paths
around the nucleus
(orbits/energy levels)
Bohr Model or Orbit Model
Neils Bohr
Bohr’s Model
• e- can only be certain distances
from the nucleus
– Only orbits of certain radii,
corresponding to specific E, can
be occupied
• Distance is based on the
amount of energy in the e– e- close to the nucleus have low
energy
– those far from the nucleus have
higher energy
Bohr’s Model
• Energy difference between
two levels = a quantum of
energy
Bohr Model/Ladder Analogy
– If you are on a low rung, do you
have low or high PE?
– Can your foot move from rung A to
rung B?
• requires energy input
– What happens to PE as you move
up the ladder?
– Can your foot be in between two
rungs?
• Energy is quantized
• Just as your foot can move between two
rungs of a ladder, e- can move (jump)
between allowed orbits
• In the transition, energy is absorbed or
released
Bohr Illustration
http://www.unm.edu/~astro1/101lab/lab5/lab5_C.html
• In the transition, energy is absorbed or
released
• The energy is emitted or absorbed as a
photon whose E = h
• The energy of each level can be
calculated using the following equation
E = -(2.18x10-18 J)(1/n2)
where n = energy level
Ground state (GS) has n = 1
Next allowed level (ES) has n = 2
etc.
• What is energy if n =1?
• n = 2?
• Notice, as n increases, E gets less
negative (less favorable)
– As you get further from nucleus, electron is
less stable
• Bohr said e- can jump between allowed
energy levels
• The energy to do this can be calculated:
∆E = -(2.18x10-18 J)(1/nf2 – 1/ni2)
where ni is the energy level you start
from and nf is the energy level you end
up in
• Calculate the energy needed to move an
electron from GS to third ES.
• Notice sign for ∆E. Does it make sense?
• Calculate the energy and  to move an
electron from n=5 to n=2.
– What should sign of energy be?
– Notice  is in visible part of spectrum.
Explanation for line spectra (next slide)
Lines are consistent with the idea that quantization limits
the possible energies allowed
wikipedia
• Bohr’s model/math could explain the
behavior of atoms with only 1 e– He could not explain the energy/colors given off
by anything with more than 1e-
• 1st Flaw: orbits are not circular (we learn this
from quantum mechanics)
– If circular, e- should lose energy as it moves and
would eventually crash into + nucleus
• 2nd Flaw: described the path of the electron
like a large moving object.
– Discredited the fact that it actually moves like a
wave. (deBroglie)
What We Keep from Bohr
• e- exist only in discrete energy levels
described by quantum numbers
• Energy is needed to promote e- to higher
energy levels
• Energy is released when e- move from
high to low energy levels
Louis de Broglie (1924)
• Electrons (particles) move like waves
– goes along with Einstein’s dual nature of light
– confined waves can only have certain frequencies
– Only a certain # waves can pass through that space in a
second
• de Broglie suggested that electrons are like
waves confined to a space around nucleus
(orbitals)
– If wavelike, they can only have certain frequencies
(or energies)
de Broglie
• The  of an e- (or any particle) depends on
its mass and velocity
 = h/mv
mv is momentum
• What is the  of an e- moving with a speed
of 5.97x106 m/s? m of e- = 9.11x10-31 kg
• If e- behaves like a wave can we determine
its position?
– a wave extends into space and its location is
not precisely defined
• Heisenberg’s Uncertainty Principle
– We can’t know both the location and
momentum of an e- (because of dual nature)
– There will be uncertainty in position, ∆x and
momentum, ∆mv
∆x · ∆mv  h/4
• Because of dual nature and uncertainty
principle…
• New atomic model is based on the idea
that we can calculate the energy of an
electron but can only describe location in
terms of probability (2) (Schrodinger)
• Enter quantum mechanics
• If e- move like waves, they have certain
frequencies
• These frequencies could correspond to the
energy levels/orbitals
Orbitals
• Regions around the nucleus that
corresponds to specific energy levels
– Electron clouds
• Regions where electrons are likely to be
found
– Cloud is more dense in regions of higher
probability
– More likely near nucleus or far from nucleus?
Why?
Solid Sphere Model or
Billiard Ball Model
John Dalton
Plum Pudding Model
J.J. Thomson
Bohr Model or Orbit Model
Neils Bohr
Planetary Model
or
Nuclear Model
Ernest Rutherford
Electron Cloud Model or
Quantum Mechanical Model
Louis de Broglie & Erwin Schrodinger
http://mhsweb.ci.manchester.ct.us/Library/webquests/atomicmodels.htm
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Bohr
Circular orbits
E quantized
Treats e- as large
moving object
Only works for 1esystems
Quantum Mechanics
• Mathematical
description of atom
• Orbitals (probable
location)
• E quantized
• Treats e- like wave