Transcript Developing an Atomic Theory Part 2

Developing an Atomic
Theory
Part 2
Review
Democritus developed the first atomic theory.
Review
Democritus developed the first atomic theory.
around 400 B.C.
Review
Democritus developed the first atomic theory.
around 400 B.C.
descriptive not functional
Review
Democritus (400 B.C.)
Review
Democritus (400 B.C.)
Dalton developed the first modern atomic theory.
Review
Democritus (400 B.C.)
Dalton developed the first modern atomic theory.
published in 1803
Review
Democritus (400 B.C.)
Dalton developed the first modern atomic theory.
published in 1803
based on observations of himself and others
Review
Democritus (400 B.C.)
Dalton developed the first modern atomic theory.
published in 1803
based on observations of himself and others
still descriptive and not functional
Review
Democritus (400 B.C.)
Dalton (1803)
Review
Democritus (400 B.C.)
Dalton (1803)
J. J. Thomson discovered the electron.
Review
Democritus (400 B.C.)
Dalton (1803)
J. J. Thomson discovered the electron.
using the cathode ray tube in 1897
Review
Democritus (400 B.C.)
Dalton (1803)
J. J. Thomson discovered the electron.
using the cathode ray tube in 1897
developed the plum pudding model
Review
Democritus (400 B.C.)
Dalton (1803)
J. J. Thomson (1897)
Review
Democritus (400 B.C.)
Dalton (1803)
J. J. Thomson (1897)
Nagaoka proposed a model with a central nucleus
for an atom.
Review
Democritus (400 B.C.)
Dalton (1803)
J. J. Thomson (1897)
Nagaoka proposed a model with a central nucleus
for an atom.
proposed in 1904
Review
Democritus (400 B.C.)
Dalton (1803)
J. J. Thomson (1897)
Nagaoka proposed a model with a central nucleus
for an atom.
proposed in 1904
not well publicized in Europe and America
Review
Democritus (400 B.C.)
Dalton (1803)
J. J. Thomson (1897)
Nagaoka (1904)
Review
Democritus (400 B.C.)
Dalton (1803)
J. J. Thomson (1897)
Nagaoka (1904)
Rutherford discovered the nucleus.
Review
Democritus (400 B.C.)
Dalton (1803)
J. J. Thomson (1897)
Nagaoka (1904)
Rutherford discovered the nucleus.
Developed the solar system model in 1911
Review
Democritus (400 B.C.)
Dalton (1803)
J. J. Thomson (1897)
Nagaoka (1904)
Rutherford (1911)
Review
Democritus (400 B.C.)
Dalton (1803)
J. J. Thomson (1897)
Nagaoka (1904)
Rutherford (1911)
That is where we left off.
Problem
There is a problem with the solar system model.
Problem
There is a problem with the solar system model.
Classical physics says that as a charged particle
moves in a circle, it emits energy.
Problem
There is a problem with the solar system model.
Classical physics says that as a charged particle
moves in a circle, it emits energy.
As the electron emits energy, its orbital energy
should decay.
Problem
There is a problem with the solar system model.
Classical physics says that as a charged particle
moves in a circle, it emits energy.
As the electron emits energy, its orbital energy
should decay.
The electron should spiral into the nucleus.
Problem
There is a problem with the solar system model.
Classical physics says that as a charged particle
moves in a circle, it emits energy.
As the electron emits energy, its orbital energy
should decay.
The electron should spiral into the nucleus.
Problem
There is a problem with the solar system model.
Classical physics says that as a charged particle
moves in a circle, it emits energy.
As the electron emits energy, its orbital energy
should decay.
The electron should spiral into the nucleus.
It should take about 1/1,000,000,000 of a second.
Problem
There is a problem with the solar system model.
Classical physics says that as a charged particle
moves in a circle, it emits energy.
As the electron emits energy, its orbital energy
should decay.
The electron should spiral into the nucleus.
It should take about 1/1,000,000,000 of a second.
But, electrons don’t spiral into the nucleus!
Problem
There is a problem with the solar system model.
We need a newer, more realistic model of the atom.
Problem
There is a problem with the solar system model.
We need a newer, more realistic model of the atom.
Here comes the quantum model.
Max Planck
Max Planck
Max Planck said that energy is
in packets he called “quanta.”
Max Planck
Max Planck said that energy is
in packets he called “quanta.”
That is, the energy in a system
increases or decreases in
steps.
Max Planck
Max Planck said that energy is
in packets he called “quanta.”
That is, the energy in a system
increases or decreases in
steps.
This is contrary to what is
predicted by classical physics.
Max Planck
Max Planck said that energy is
in packets he called “quanta.”
That is, the energy in a system
increases or decreases in
steps.
This is contrary to what is
predicted by classical physics.
Today, we call those energy
packets photons.
Max Planck
The energy in a photon depends
on the frequency of the light.
Max Planck
The energy in a photon depends
on the frequency of the light.
Energy, E, is equal to a
constant, h, (Planck’s
constant), times the
frequency of the light, ν
(lower case Greek letter nu).
Max Planck
The energy in a photon depends
on the frequency of the light.
Energy, E, is equal to a
constant, h, (Planck’s
constant), times the
frequency of the light, ν
(lower case Greek letter nu).
E = hν
Max Planck
The energy in a photon depends
on the frequency of the light.
Energy, E, is equal to a
constant, h, (Planck’s
constant), times the
frequency of the light, ν
(lower case Greek letter nu).
E = hν
Presented in 1900.
Albert Einstein
Albert Einstein
Albert Einstein made use of
these quanta to explain the
photoelectric effect.
Albert Einstein
The photoelectric effect:
Albert Einstein
The photoelectric effect:
If we shine blue light on
the surface of a piece of
metal, electrons are ejected
from the metal.
Albert Einstein
The photoelectric effect:
If we shine blue light on
the surface of a piece of
metal, electrons are ejected
from the metal.
Albert Einstein
The photoelectric effect:
If we shine red light on the
surface of a piece of metal,
no electrons are ejected
from the metal.
Albert Einstein
The photoelectric effect:
If we shine red light on the
surface of a piece of metal,
no electrons are ejected
from the metal.
Albert Einstein
In 1905, Einstein published
four papers that contributed
substantially to the
foundations of modern
physics.
Albert Einstein
In 1905, Einstein published
four papers that contributed
substantially to the
foundations of modern
physics.
The first one published
focused on the photoelectric
effect.
Albert Einstein
Einstein said that we needed
to look at light as a particle,
not as a wave.
Albert Einstein
Einstein said that we needed
to look at light as a particle,
not as a wave.
Blue light has a higher
frequency, ν, than red light.
Albert Einstein
Einstein said that we needed
to look at light as a particle,
not as a wave.
If we look at light as a wave,
then we only see more crests
of a blue wave hitting the
metal surface than crests of a
red wave.
Albert Einstein
Einstein said that we needed
to look at light as a particle,
not as a wave.
If we look at light as a wave,
then we only see more crests
of a blue wave hitting the
metal surface than crests of a
red wave.
The average energy stays the
same.
Albert Einstein
Einstein said that we needed
to look at light as a particle,
not as a wave.
If we look at light as a
particle, then we see blue
photons hitting the metal
surface with more energy
than red photons.
Albert Einstein
Einstein said that we needed
to look at light as a particle,
not as a wave.
If we look at light as a
particle, then we see blue
photons hitting the metal
surface with more energy
than red photons.
The higher energy removes
the electrons.
Albert Einstein
Einstein taught us that light
could be thought of as both a
wave and as a particle.
Neils Bohr
Neils Bohr
Neils Bohr was a Danish
student of physics.
Niels Bohr
Niels Bohr was a Danish
student of physics.
He had heard of Rutherford’s
experiments.
Niels Bohr
Niels Bohr was a Danish
student of physics.
He had heard of Rutherford’s
experiments.
He studied with Rutherford
and improved on the solar
system model.
Niels Bohr
Bohr knew that each element
had a characteristic spectrum.
Niels Bohr
Bohr knew that each element
had a characteristic spectrum.
Niels Bohr
Bohr knew that each element
had a characteristic spectrum.
Elements produce light at
particular frequencies when
the element is heated.
Niels Bohr
Bohr knew that each element
had a characteristic spectrum.
Elements produce light at
particular frequencies when
the element is heated.
They also absorb light of the
same frequencies when white
light is shined through a cloud
of the gaseous element.
Niels Bohr
With these observations and
the solar system model, Bohr
proposed his own model in
1913.
Niels Bohr
Electrons are found only in
specific circular paths (orbits)
around the nucleus.
Niels Bohr
electron
nucleus
orbit
Niels Bohr
As atoms absorb light, the
electrons move from a low
energy orbit (ground state) to
a high energy orbit (excited
state).
Niels Bohr
photon in
Niels Bohr
Niels Bohr
Niels Bohr
The energy of the photon,
Ephoton, must be exactly right.
Niels Bohr
It must exactly match the
energy difference, ∆E, between
the orbitals.
Niels Bohr
photon in
∆E
Ephoton
Ephoton = ∆E
Niels Bohr
If Ephoton is not exactly equal to
∆E, the photon does not
interact with the atom.
Niels Bohr
Niels Bohr
As the electrons move from a
high energy orbit (excited
state) to a lower energy orbit,
they emit light.
Niels Bohr
Niels Bohr
photon out
Niels Bohr
The energy of the photon
emitted, Ephoton, is exactly
equal to the energy difference,
∆E, between the orbitals.
Niels Bohr
We can determine the
energies of the orbitals by
measuring the energies of the
photons absorbed and emitted
by the elements.
Niels Bohr
We can use atomic spectra
data to learn that the Bohr
orbits are not spaced evenly in
energy.
Niels Bohr
As the orbits increase in
energy (as the orbits move
away from the nucleus), the
difference in energy, ∆E,
between orbits decreases.
Niels Bohr
Louis de Broglie
Louis de Broglie
In 1923, Louis de Broglie (in his
Ph.D. dissertation) proposed
that moving particles, such as
the electron, could be thought of
as waves.
Louis de Broglie
In 1923, Louis de Broglie (in his
Ph.D. dissertation) proposed
that moving particles, such as
the electron, could be thought of
as waves.
This allowed us to start to
understand why electrons were
confined to specific orbitals.
Louis de Broglie
In 1923, Louis de Broglie (in his
Ph.D. dissertation) proposed
that moving particles, such as
the electron, could be thought of
as waves.
The electrons circle the nucleus
as waves.
Louis de Broglie
In 1923, Louis de Broglie (in his
Ph.D. dissertation) proposed
that moving particles, such as
the electron, could be thought of
as waves.
The electrons circle the nucleus
as waves.
If the waves interact in just the
right way, they will reinforce
each other and be stable.
Louis de Broglie
In 1923, Louis de Broglie (in his
Ph.D. dissertation) proposed
that moving particles, such as
the electron, could be thought of
as waves.
The electrons circle the nucleus
as waves.
If the waves interfere with
themselves, they will be
unstable.
Louis de Broglie
This is what they look like.
Erwin Schrödinger
Erwin Schrödinger
In 1926, Erwin Schrödinger
developed mathematical
equations to describe the
motion of the electrons in
atoms.
Erwin Schrödinger
In 1926, Erwin Schrödinger
developed mathematical
equations to describe the
motion of the electrons in
atoms.
This became known as the
Schrödinger Equation.
Erwin Schrödinger
The Schrödinger Equation:
Erwin Schrödinger
The Schrödinger Equation:
Erwin Schrödinger
The Schrödinger Equation:
It describes the position of the
electron in terms of Total
Energy and Potential Energy.
Erwin Schrödinger
The Schrödinger Equation:
The equation gives the position
as a likelihood - a probability.
Erwin Schrödinger
The Schrödinger Equation:
This then leads to the concept of
the orbital as an electron cloud.
Werner Heisenberg
Werner Heisenberg
In 1927, the year after
Schrödinger published his
equation, Werner Heisenberg
determined the amount of
uncertainty in the calculations
about the position of an electron
in an atom.
Werner Heisenberg
In 1927, the year after
Schrödinger published his
equation, Werner Heisenberg
determined the amount of
uncertainty in the calculations
about the position of an electron
in an atom.
This is the Heisenberg
Uncertainty Principle.
Werner Heisenberg
The Heisenberg Uncertainty
Principle:
Werner Heisenberg
The Heisenberg Uncertainty
Principle:
We have limits on our ability
to observe things at very small
scales.
Werner Heisenberg
The Heisenberg Uncertainty
Principle:
We have limits on our ability
to observe things at very small
scales.
If we know the position of an
electron (at a particular time)
very well, then we cannot
know its velocity (at that time)
very well.
Summary
Summary
Planck introduced the idea of quantized energy in
1900.
Summary
Planck (1900)
Summary
Planck (1900)
Einstein showed how to use quata (photons) to
explain the photoelectric effect in 1905.
Summary
Planck (1900)
Einstein (1905)
Summary
Planck (1900)
Einstein (1905)
Bohr introduced the idea of an atom with fixed
circular orbits in 1913.
Summary
Planck (1900)
Einstein (1905)
Bohr (1913)
Summary
Planck (1900)
Einstein (1905)
Bohr (1913)
de Broglie proposed that electrons could be thought
of as waves in 1923.
Summary
Planck (1900)
Einstein (1905)
Bohr (1913)
de Broglie (1923)
Summary
Planck (1900)
Einstein (1905)
Bohr (1913)
de Broglie (1923)
Schrödinger derived an equation to determine the
position of an electron in an atom in 1926.
Summary
Planck (1900)
Einstein (1905)
Bohr (1913)
de Broglie (1923)
Schrödinger (1926)
Summary
Planck (1900)
Einstein (1905)
Bohr (1913)
de Broglie (1923)
Schrödinger (1926)
Heisenberg determined the level of uncertainty that
exists in measurements at the atomic level in 1927.
Summary
Planck (1900)
Einstein (1905)
Bohr (1913)
de Broglie (1923)
Schrödinger (1926)
Heisenberg (1927)