4.1 Refinements of the
Atomic Model
Mr. Chris Walters
Williamstown Schools
The Dual Nature of Light
• Experimentation has shown that light
behaves as both a wave (energy) and as a
particle (matter).
• This concept seems to defy logic but is
supported.
• “A form of energy that displays
wavelike behavior as it travels
through space”
• Travels at 3.0 x 108 m/sec in a
vacuum (c)
Has the measurable properties of wavelength()
and frequency ()
The speed of light is equal to the product of
wavelength times frequency.
c=λ •ν
All the wavelengths of light form a CONTINUOUS
SPECTRUM
FREQUENCY is measured in HERTZ (Hz). A Hz is one
wave occurring per second.
Visible Light
• that portion of the
electromagnetic
spectrum from
wavelengths 375 nm
to 725 nm
• Illustrated in 7 colors
ROY G BIV (from
longest wavelength to
shortest)
Light as Particles
• The wave theory of light
encountered two problems
– It predicted that heated objects
would give off ultraviolet light, they
emit visible light
– It could not explain the
Photoelectric effect
Photoelectric Effect
• The Photoelectric
effect is the emission
of electrons by metals
when light shines on
them
– Only certain
frequencies of light
caused the effect
Explanation - Planck
• Max Planck (1858-1947)
proposed that energy was
given off in specific
quantities or Quanta.
(singular: Quantum)
• Planck proposed the
following equation E= h,
where h was a constant
value.
• Planck’s constant (h) =
6.626 x 10 -34
Continuation - Einstein
• An individual particle
of light is called a
photon.
• Einstein proposed that
absorption of photons
at certain quanta
explained the
photoelectric effect.
Exciting Electrons to
release light
• When atoms in the gaseous state are heated
they increase in PE then return to original
state as they emit light.
– As they are heated the electrons leave the
ground state and become excited.
– They give off light in specific amounts
(quanta).
– This can be illustrated in the line spectrum
Bohr Model of the Atom
• Niels Bohr (1885-1962)
proposed a model using
this new information.
• It showed the orbits of the
electrons a specific
quantized distances from
the nucleus.
• Bohr’s model worked well
on Hydrogen, but failed to
match data with more
complicated atoms and
their line spectra.
Spectroscopy
• A spectroscope is an
instrument that
separates light into a
spectrum that can be
analyzed.
• This allows the light to
be examined and its
atomic source
discovered.
Quantum Model
• Replaced the orbits of Bohr with regions of
space in which the electrons are located
called orbitals.
• Orbitals are quantized.
• Quantum theory mathematically explains
the wave properties of electrons and other
small particles.
Louis deBroglie
• Louis deBroglie (18921987) proposed the dual
nature of electrons.
Schrodinger’s Wave Equation
• Erwin Schrödinger
proposed his wave
equation that
mathematically explains
electron action.
Heisenberg’s Uncertainty Principle
• Werner Heisenberg
contributed his
Uncertainty Principle
which states it is not
possible to know both the
velocity and position of a
particle at the same time.