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Transcript
The Development of a New
Atomic Model
Rutherford- did not explain how
the atom’s negatively charged
particles are distributed in the
space surrounding it’s positively
charged nucleus.
The New Atomic Model
• Researcher used investigations into the
absorption and emission of light
• Studies revealed a relationship beteen
light an atom’s electrons
• New understanding about the nature of
energy, matter, and atomic structure.
Properties of Light
• Before 1900, light was thought to behave solely
as a wave
– Wavelike description
• It is type of electromagnetic radiation
• Forms part of the electromagnetic spectrum
• Significant wavelike motion characterized by wavelength and
frequency
– Wavelength (λ) is the distance between corresponding points
on adjacent waves.
– Frequency (v) is the number of waves that pass a specific point
in a given time, usually one minute.
Frequency and wavelength are
mathematically related to each other
• c=λv c is the speed of light, a constant
• There for λ, wavelength in m, is inversely
proportional to v, frequency in s-1.
• As wavelength decreases frequency
increases and vice versa
The Photoelectric Effect
• The photoelectric effect refers to the
emission of electron when light is shines
on a metal.
The Photoelectric Effect
• The mystery was…..
• No electron would be emmited if the lights
frequency (v) was below a certain
minimum.
• No matter how intense (W) the light was.
• Wave theory state that light of any
frequency could supply enough energy to
eject an electron.
The Particle Description of Light
• Max Planck (1900 German Physicist)
– Studied emission of light by hot objects
– He proposed the hot objects do not emit
electromagnetic energy continuously (as
would be expected if all we were dealing with
was a wave)
The Particle Description of Light
• Quantum- a measure of energy that is the
minimum quantity of energy that can be lost or
gain by an atom
• Planck proposed a relationship between a
quantum of energy and the frequency of
radiation
• E=hv
• E= energy in joules, v is frequency (s-1),
• h= a fundamental physical constant now know
as Planck’s constant = 6.626x 10 -34
The Duality of particles and waves
• Albert Einstein expanded on Planck’s work and
proposed a radical idea
• Electromagnetic radiation has a dual waveparticle nature
• While like light act like a wave
• It is a stream of particles
• Each particle carries a quantum of energy
• These particles are called photons
– These particles have zero mass but carry a quantum
of energy
This explained the photoelectric
effect
• Einstein explained
– Electromagnetic radiation is only absorbed by
matter in whole numbers
– In order for an electron to be rejected from the
surface of the metal it must be struck by a
single photon possessing at least a minimum
energy required to knock the electron off.
– Every metal has a different frequency
Home work
• Pages 124-125
– #1-25
– Complete sentences
– If it is a multiple choice problem, select the
letter choice them write a true complete sence
out of the question and the choice: DO NOT
COPY THE QUESTIONS
– If it is a calculation, show equation used and
ALL work
– Have a great Thanksgiving!!!