Quantum Model of the AtomQuantum Model of the Atom

BohrBohr de Brogliede Broglie Heisenberg Heisenberg SchrödingerSchrödinger

Neils Bohr (1885 –1962)Neils Bohr (1885 –1962)

Bohr Model Bohr Model of the of the

Hydrogen Hydrogen AtomAtom

Bohr model of the atomBohr model of the atom

In the Bohr In the Bohr model, model,

electrons electrons can only can only exist at exist at specific specific

energy levels energy levels (orbit).(orbit).

Energy

Photo Absorption and Emission

Hydrogen Line SpectrumHydrogen Line Spectrum

Balmer Series

Line SpectraLine Spectra

Line spectrum of Hydrogen is Line spectrum of Hydrogen is produced when an electron produced when an electron drops from a higher-energy drops from a higher-energy orbit to a lower energy orbit.orbit to a lower energy orbit.

Specifically, Specifically,

EEphotonphoton = E = E2 2 - E- E11 = h = h

Bohr Checked it with Math.Bohr Checked it with Math.

Used mass and charge of the Used mass and charge of the electron together with Planck’s electron together with Planck’s constant and calculated where constant and calculated where the spectral lines should be and the spectral lines should be and they were!they were!

Problem -- only worked for Problem -- only worked for Hydrogen!Hydrogen!

Bohr model of the atomBohr model of the atom The Bohr model is a The Bohr model is a

‘planetary’ type ‘planetary’ type model.model.

Each principal Each principal quantum represents quantum represents a new ‘orbit’ or layer.a new ‘orbit’ or layer.

The nucleus is at the The nucleus is at the center of the model.center of the model.

Hydrogen Spectrum (cont.)Hydrogen Spectrum (cont.)

Each line of the Hydrogen Each line of the Hydrogen spectrum is produced by spectrum is produced by and corresponds to the and corresponds to the

emission of photons with emission of photons with specific energies (E = hspecific energies (E = h))

Bohr Model Bohr Model

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What the Heck is Light?

Hold It!Hold It! Nay, Nay says “Classical” Nay, Nay says “Classical”

theory.theory. Hydrogen should be excited by Hydrogen should be excited by

whatever amount of energy.whatever amount of energy. Should be continuous spectrumShould be continuous spectrum What’s with the lines????What’s with the lines????

Why wouldn’t there be an Why wouldn’t there be an infinite number of energy levels infinite number of energy levels for electrons?for electrons?

Photoelectric effect and Photoelectric effect and Hydrogen spectrum.Hydrogen spectrum.

Neils Bohr (1885 –1962)Neils Bohr (1885 –1962)

Bohr Model Bohr Model of the of the

Hydrogen Hydrogen AtomAtom

Louis de Broglie Louis de Broglie (1892-1987)(1892-1987)

Electrons should Electrons should be considered be considered

waves confined waves confined to the space to the space around an around an

atomic nucleusatomic nucleus

The Quantum Atom (cont.)The Quantum Atom (cont.)

Since electrons are waves, Since electrons are waves, they can amplify and cancel they can amplify and cancel out when in and out of sync.out when in and out of sync.

Therefore only certain Therefore only certain energies of electrons are energies of electrons are possible.possible.

Werner HeisenbergWerner Heisenberg

Heisenberg Heisenberg Uncertainty Uncertainty

Principle – It is Principle – It is impossible to impossible to determine the determine the position and position and velocity of an velocity of an

electron electron simultaneously.simultaneously.

Separated at Birth….Separated at Birth….

Heisenberg uncertainty Heisenberg uncertainty principleprinciple

In order to observe an electron, In order to observe an electron, one would need to hit it with one would need to hit it with photons having a very short photons having a very short wavelength.wavelength.

Short wavelength photons Short wavelength photons would have a high frequency would have a high frequency and a great deal of energy.and a great deal of energy.

Heisenberg uncertainty Heisenberg uncertainty principleprinciple

If one were to hit an electron, it If one were to hit an electron, it would cause the motion and the would cause the motion and the speed of the electron to change.speed of the electron to change.

Lower energy photons would Lower energy photons would have a smaller effect but would have a smaller effect but would not give precise information.not give precise information.

Heisenberg Uncertainty Heisenberg Uncertainty PrinciplePrinciple

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Erwin Schrödinger Erwin Schrödinger (1887-1961)(1887-1961)

Schrödinger Schrödinger developed the developed the

calculus to calculus to describe the describe the

wavewave behavior behavior and energies of and energies of

electrons in electrons in atoms.atoms.

Schrödinger’s EquationSchrödinger’s Equation

Yeah, but Yeah, but it works!it works!

Bohr vs. Schrödinger Bohr vs. Schrödinger Orbits vs. OrbitalsOrbits vs. Orbitals

Bohr -- definite Bohr -- definite distinct distinct orbitsorbits populated by populated by

electron electron particles.particles.

Bohr vs. Schrödinger Bohr vs. Schrödinger Orbits vs. OrbitalsOrbits vs. Orbitals

Schrödinger -- electron are Schrödinger -- electron are waves (de Broglie) with a waves (de Broglie) with a

certain probability certain probability (mathematical model) of (mathematical model) of

being found in three being found in three dimensional regions around dimensional regions around

the nucleus - orbitalsthe nucleus - orbitals

Comparing Models of the Comparing Models of the Atom – A reviewAtom – A review

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