Developing an Atomic Theory

The Quantum Experience

Developing an Atomic Theory

Part 2

ReviewDemocritus developed the first atomic theory.

ReviewDemocritus developed the first atomic theory.

around 400 B.C.

ReviewDemocritus developed the first atomic theory.

around 400 B.C.

descriptive not functional

ReviewDemocritus (400 B.C.)

ReviewDemocritus (400 B.C.)

Dalton developed the first modern atomic theory.

ReviewDemocritus (400 B.C.)

Dalton developed the first modern atomic theory.

published in 1803

ReviewDemocritus (400 B.C.)

Dalton developed the first modern atomic theory.

published in 1803

based on observations of himself and others

ReviewDemocritus (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

ReviewDemocritus (400 B.C.)

Dalton (1803)

ReviewDemocritus (400 B.C.)

Dalton (1803)

J. J. Thomson discovered the electron.

ReviewDemocritus (400 B.C.)

Dalton (1803)

J. J. Thomson discovered the electron.

using the cathode ray tube in 1897

ReviewDemocritus (400 B.C.)

Dalton (1803)

J. J. Thomson discovered the electron.

using the cathode ray tube in 1897

developed the plum pudding model

ReviewDemocritus (400 B.C.)

Dalton (1803)

J. J. Thomson (1897)

ReviewDemocritus (400 B.C.)

Dalton (1803)

J. J. Thomson (1897)

Nagaoka proposed a model with a central nucleus for an atom.

ReviewDemocritus (400 B.C.)

Dalton (1803)

J. J. Thomson (1897)

Nagaoka proposed a model with a central nucleus for an atom.

proposed in 1904

ReviewDemocritus (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

ReviewDemocritus (400 B.C.)

Dalton (1803)

J. J. Thomson (1897)

Nagaoka (1904)

ReviewDemocritus (400 B.C.)

Dalton (1803)

J. J. Thomson (1897)

Nagaoka (1904)

Rutherford discovered the nucleus.

ReviewDemocritus (400 B.C.)

Dalton (1803)

J. J. Thomson (1897)

Nagaoka (1904)

Rutherford discovered the nucleus.

Developed the solar system model in 1911

ReviewDemocritus (400 B.C.)

Dalton (1803)

J. J. Thomson (1897)

Nagaoka (1904)

Rutherford (1911)

ReviewDemocritus (400 B.C.)

Dalton (1803)

J. J. Thomson (1897)

Nagaoka (1904)

Rutherford (1911)

That is where we left off.

ProblemThere is a problem with the solar system model.

ProblemThere is a problem with the solar system model.

Classical physics says that as a charged particle moves in a circle, it emits energy.

ProblemThere 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.

ProblemThere 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.

ProblemThere 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.

ProblemThere 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.

ProblemThere 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!

ProblemThere is a problem with the solar system model.

We need a newer, more realistic model of the atom.

ProblemThere 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 PlanckMax Planck said that energy is in packets he called “quanta.”

Max PlanckMax Planck said that energy is in packets he called “quanta.”

That is, the energy in a system increases or decreases in steps.

Max PlanckMax 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 PlanckMax 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 PlanckThe energy in a photon depends on the frequency of the light.

Max PlanckThe 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 PlanckThe 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 PlanckThe 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 EinsteinAlbert Einstein made use of these quanta to explain the photoelectric effect.

Albert EinsteinThe photoelectric effect:

Albert EinsteinThe photoelectric effect:

If we shine blue light on the surface of a piece of metal, electrons are ejected from the metal.

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.

Albert Einstein

Niels Bohr

Niels BohrNeils Bohr was a Danish student of physics.

Niels BohrNiels Bohr was a Danish student of physics.

He had heard of Rutherford’s experiments.

Niels BohrNiels 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 BohrBohr knew that each element had a characteristic spectrum.

Niels BohrBohr knew that each element had a characteristic spectrum.

Niels BohrBohr knew that each element had a characteristic spectrum.

Elements produce light at particular frequencies when the element is heated.

Niels BohrBohr 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 BohrWith these observations and the solar system model, Bohr proposed his own model in 1913.

Niels BohrElectrons are found only in specific circular paths (orbits) around the nucleus.

Niels Bohr

electron

orbit

nucleus

Niels BohrAs 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 BohrThe energy of the photon, Ephoton, must be exactly right.

It must exactly match the energy difference, ∆E, between the orbitals.

Niels Bohr

Niels Bohr

∆Ephoton in

Ephoton

Ephoton = ∆E

If Ephoton is not exactly equal to ∆E, the photon does not interact with the atom.

Niels Bohr

Niels Bohr

Niels BohrAs 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 BohrThe energy of the photon emitted, Ephoton, is exactly equal to the energy difference, ∆E, between the orbitals.

We can determine the energies of the orbitals by measuring the energies of the photons absorbed and emitted by the elements.

Niels Bohr

Niels BohrWe can use atomic spectra data to learn that the Bohr orbits are not spaced evenly in energy.

Niels BohrAs 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 BroglieIn 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 BroglieIn 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 orbits.

Louis de BroglieIn 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 BroglieIn 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 BroglieIn 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 BroglieThis is what they look like.

Erwin Schrödinger

Erwin SchrödingerIn 1926, Erwin Schrödinger developed mathematical equations to describe the motion of the electrons in atoms.

Erwin SchrödingerIn 1926, Erwin Schrödinger developed mathematical equations to describe the motion of the electrons in atoms.

This became known as the Schrödinger Equation.

Erwin SchrödingerIn 1926, Erwin Schrödinger developed mathematical equations to describe the motion of the electrons in atoms.

“Where did we get that [Schrödinger's equation] from? It's not possible to derive it from anything you know. It came out of the mind of Schrödinger.” Richard Feynman

Erwin SchrödingerThe Schrödinger Equation:

Erwin SchrödingerThe Schrödinger Equation:

Erwin SchrödingerThe Schrödinger Equation:

It describes the position of the electron in terms of Total Energy and Potential Energy.

Erwin SchrödingerThe Schrödinger Equation:

The equation gives the position as a likelihood - a probability.

Erwin SchrödingerThe Schrödinger Equation:

This then leads to the concept of the orbital as an electron cloud.

Werner Heisenberg

Werner HeisenbergIn 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 HeisenbergIn 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 HeisenbergThe Heisenberg Uncertainty Principle:

Werner HeisenbergThe Heisenberg Uncertainty Principle:

We have limits on our ability to observe things at very small scales.

Werner HeisenbergThe 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.

James Chadwick

James ChadwickExperiments in Germany and France showed that the nucleus of the atom contained more than just protons.

James ChadwickExperiments in Germany and France showed that the nucleus of the atom contained more than just protons.

Rutherford felt that the additional particles were “dual particles” composed of protons and orbiting electrons.

James ChadwickExperiments in Germany and France showed that the nucleus of the atom contained more than just protons.

Rutherford felt that the additional particles were “dual particles” composed of protons and orbiting electrons.

The data did not support this.

James ChadwickIn 1932, James Chadwick, at Cambridge University, proposed that the unknown particle had

James ChadwickIn 1932, James Chadwick, at Cambridge University, proposed that the unknown particle had

a mass slightly larger than the proton

no charge

James ChadwickIn 1932, James Chadwick, at Cambridge University, proposed that the unknown particle had

a mass slightly larger than the proton

no charge

He designed and performed the experiments to verify this.

James ChadwickThis new particle was named the “neutron.”

James ChadwickThis new particle was named the “neutron.”

James Chadwick received the Nobel Prize in Physics in 1935 for his research.

Summary

SummaryPlanck introduced the idea of quantized energy in 1900.

SummaryPlanck (1900)

SummaryPlanck (1900)

Einstein showed how to use quata (photons) to explain the photoelectric effect in 1905.

SummaryPlanck (1900)

Einstein (1905)

SummaryPlanck (1900)

Einstein (1905)

Bohr introduced the idea of an atom with fixed circular orbits in 1913.

SummaryPlanck (1900)

Einstein (1905)

Bohr (1913)

SummaryPlanck (1900)

Einstein (1905)

Bohr (1913)

de Broglie proposed that electrons could be thought of as waves in 1923.

SummaryPlanck (1900)

Einstein (1905)

Bohr (1913)

de Broglie (1923)

SummaryPlanck (1900)

Einstein (1905)

Bohr (1913)

de Broglie (1923)

Schrödinger derived an equation to determine the position of an electron in an atom in 1926.

SummaryPlanck (1900)

Einstein (1905)

Bohr (1913)

de Broglie (1923)

Schrödinger (1926)

SummaryPlanck (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.

SummaryPlanck (1900)

Einstein (1905)

Bohr (1913)

de Broglie (1923)

Schrödinger (1926)

Heisenberg (1927)

SummaryPlanck (1900)

Einstein (1905)

Bohr (1913)

de Broglie (1923)

Schrödinger (1926)

Heisenberg (1927)

Chadwick discovers the neutron in 1932.

Summary

Planck (1900)

Einstein (1905)

Bohr (1913)

de Broglie (1923)

Schrödinger (1926)

Heisenberg (1927)

Chadwick (1932)