Transcript DOC - islcs

Later Contributors to
Atomic Theory
Pg. 90-94
2nd Note Taking Sheet
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Interaction of Light and Matter
• In order to understand the contributions of the
next scientist, it is important to understand the
characteristics of light and how it can interact
with matter.
• Other names for light are radiant energy or
electromagnetic radiation (emr for short).
• In the early 1900s there were observable
phenomena involving light and its interaction
with matter that could not be explained.
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Electromagnetic Radiation
• Light consists of an oscillating electric field
at right angles to an oscillating magnetic
field, thus its name (emr).
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Characteristics of Light
(p.92-93)
• In order to understand the contributions of the next
scientist, it is important to understand the characteristics
of light and how it can interact with matter.
• At this time in history scientists thought of light as waves
that propagated (moved) outward perpendicular from the
source.
• In a vacuum scientists knew that light in a vacuum
traveled at 2.998 x 108 m/s.
• This maximum limit on the speed of light is a universal
constant represented by the letter “c”.
• All types of light travel at this speed in a vacuum.
• If light travels through a denser material it will slow down
and different energies of light will be bent differently.
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Characteristics of Light Continued
• The electromagnetic radiation spectrum is
all the possible energies of light.
– Note that humans can see only a very small portion of
emr called the visible range.
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Characteristics of Light Continued
Wavelength
• Light of a certain energy has a characteristic
frequency and wavelength.
• A wavelength is the distance from
peak to peak or
trough to trough.
• It is a length
measurement.
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Characteristics of Light Continued
Frequency
• The frequency of light is the number of
wavelengths that can pass through a point in a
second.
• Frequency has units of 1/s or s-1 or Hertz (Hz)
• The higher the
frequency the
higher the energy
of the light
©2011 University of Illinois Board of
Trustees •
http://islcs.ncsa.illinois.edu/copyright
Characteristics of Light Continued
Speed
• In a vacuum all light travels at 2.998 x 108 m/s
• The speed of light, its frequency and
wavelength are all related by the equation:
C=λ∙ν
Where λ (“lambda”) is wavelength and
ν (“nu”) is the frequency
• Note that if frequency becomes greater the
wavelength becomes smaller.
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Electromagnetic Radiation
Spectrum
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Characteristics of Light Continued
Energy
• In 1901 Max Planck found that atoms can only
adsorb and emit energy in distinct quantities; this
showed that energy is quantized. He also
determined that the energy of the light is given
by the equation
E=h∙ν
Where E is energy (J)
h is Planck's constant = 6.626 x 10-34 J∙s
V is the frequency in Hz or 1/s or s-1 or cycles/sec
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Inexplicable New Evidence
• Photoelectric effect
occurs when light hits a
piece of metal and the
metal ejects an
electron.
• The energy of the light
had to be at least a
certain minimum value
that was different for
different metals.
• Black body radiation.
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Albert Einstein (1905)
• To explain the photoelectric effect, in 1905
Einstein suggested that light can behave
like particles as well as waves.
• The way in which you consider light
depends on the phenomenon you are
observing. This is known as the dual
nature of light.
• Light can be considered to be
little discrete packets of energy
called photons.
©2011 University of Illinois Board of Trustees •
http://islcs.ncsa.illinois.edu/copyright
Hydrogen Line Emission Spectrum
• Scientist were very
surprised that they didn’t
get a continuous spectrum
for the light emitted by
hydrogen.
©2011 University of Illinois Board of Trustees •
http://islcs.ncsa.illinois.edu/copyright
There is a fingerprint line emission
spectrum for all the elements.
Use the spectroscope to see the emission
spectrum of other elements.
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Neils Bohr (1913)
• Explained the
unexpected result of a
hydrogen line emission
spectrum.
• Proposed a model of the
atom in which the
electrons have
quantized energy.
• Electrons of an atom
could only be certain
allowed distances from
the nucleus which
corresponded to specific
energy values.
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Bohr Continued
• When electrons are in their lowest energy
state, Bohr called this their ground state.
• He said the when electrons are in a higher
energy orbit, they are in the excited state.
• Energy is absorbed to excite an electron
and released when an electron goes back
to its ground state.
• Energy is released in the form of light.
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Hydrogen Line Emission Spectrum
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Louis DeBroglie (1923)
• In writing his doctoral thesis
Louis DeBroglie suggested
that electrons could behave
like waves as well as
particles.
• In fact he stated that all
matter has a wave nature
given by the formula
λ = h/mv
Where m is the mass and v
is the speed.
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Louis DeBroglie Continued
• This meant that an electron “orbiting” the
nucleus can be thought of as a wave.
Each electron moves with a characteristic
energy.
• The energy of the electron depends on the
wavelength.
• All matter has a characteristic wave called
a matter wave – even you!
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Erwin Schrodinger (1926)
• Schrodinger developed a
wave theory about how
electrons can exist in
atoms.
• His wave theory explains
the different energy states
of an electron and is based
on electrons behaving as
waves.
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright
Warner Heisenberg (1927)
• Realized that if
electrons behave as
waves their existence
is more spread out
and it is impossible to
know exactly where
the electron is or how
fast it is moving.
• This is a statement of
the uncertainty
principle.
©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright