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Chapter 4 – The Address of the Electron!)

2ELECTROMAGNETIC ELECTROMAGNETIC

RADIATIONRADIATIONELECTROMAGNETIC ELECTROMAGNETIC

RADIATIONRADIATION

3Electromagnetic radiation.

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Electromagnetic Electromagnetic RadiationRadiation

Electromagnetic Electromagnetic RadiationRadiation

• Most subatomic particles behave as Most subatomic particles behave as PARTICLES and obey the physics of PARTICLES and obey the physics of waves.waves.

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wavelength Visible light

wavelength

Ultaviolet radiation

Amplitude

Node

Electromagnetic Electromagnetic RadiationRadiation

Electromagnetic Electromagnetic RadiationRadiation

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• Waves have a frequencyWaves have a frequency

• Use the Greek letter “nu”, Use the Greek letter “nu”, , for frequency, , for frequency, and units are “cycles per sec”and units are “cycles per sec”

• All radiation: All radiation: • • = c = cwhere c = velocity of light = 3.00 x 10where c = velocity of light = 3.00 x 1088 m/sec m/sec

Electromagnetic Electromagnetic RadiationRadiation

Electromagnetic Electromagnetic RadiationRadiation

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Electromagnetic Electromagnetic SpectrumSpectrum

Electromagnetic Electromagnetic SpectrumSpectrum

Long wavelength --> small frequencyLong wavelength --> small frequency

Short wavelength --> high frequencyShort wavelength --> high frequency

increasing increasing frequencyfrequency

increasing increasing wavelengthwavelength

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ElectroElectromagneticmagnetic SpectrumSpectrum

ElectroElectromagneticmagnetic SpectrumSpectrum

In increasing energy, RIn increasing energy, ROOYY GG BBIIVV

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Atomic Line Emission Atomic Line Emission Spectra and Niels BohrSpectra and Niels BohrAtomic Line Emission Atomic Line Emission

Spectra and Niels BohrSpectra and Niels Bohr

Bohr’s greatest contribution to Bohr’s greatest contribution to science was in building a science was in building a simple model of the atom. It was simple model of the atom. It was based on an understanding of based on an understanding of thethe LINE EMISSION LINE EMISSION SPECTRASPECTRA of excited atoms.of excited atoms.

• Problem is that the model only Problem is that the model only works for Hworks for H

Niels BohrNiels Bohr

(1885-1962)(1885-1962)

10Excited Gases & Atomic Excited Gases & Atomic StructureStructure

Fireworks & Neon Lights illustrate bright-line spectra

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Spectrum of White Spectrum of White LightLight

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Line Emission Spectra Line Emission Spectra of Excited Atomsof Excited Atoms

Line Emission Spectra Line Emission Spectra of Excited Atomsof Excited Atoms

• Excited atoms emit light of only certain wavelengths

• The wavelengths of emitted light depend on the element.

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Spectrum of Spectrum of Excited Hydrogen GasExcited Hydrogen Gas

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Line Spectra of Other Line Spectra of Other ElementsElements

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The Electric The Electric PicklePickle

• Excited atoms can emit light.

• Here the solution in a pickle is excited electrically. The Na+ ions in the pickle juice give off light characteristic of that element.

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Light Spectrum Lab! Slit that Slit that allows light allows light insideinside

Line up the slit so Line up the slit so that it is parallel with that it is parallel with the spectrum tube the spectrum tube (light bulb)(light bulb)

ScaleScale

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Light Spectrum Lab!

• Run electricity through various gases, creating light

• Look at the light using a spectroscope to separate the light into its component colors

• Using colored pencils, draw the line spectra (all of the lines) and determine the wavelength of the three brightest lines

• Once you line up the slit with the light, then look to the scale on the right. You should see the colored lines under the scale.

Slit that Slit that allows light allows light insideinside

EyepieceEyepiece

ScaleScale

18Light Spectrum Lab!

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Atomic SpectraAtomic SpectraAtomic SpectraAtomic Spectra

+Electronorbit

One view of atomic structure in early 20th One view of atomic structure in early 20th century was that an electron (e-) traveled century was that an electron (e-) traveled about the nucleus in an orbit.about the nucleus in an orbit.

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Atomic Spectra and Atomic Spectra and BohrBohr

Atomic Spectra and Atomic Spectra and BohrBohr

Bohr said classical view is wrong. Bohr said classical view is wrong.

Need a new theory — now called Need a new theory — now called QUANTUMQUANTUM or or WAVE MECHANICSWAVE MECHANICS..

e- can only exist in certain discrete e- can only exist in certain discrete orbitsorbits

e- is restricted to e- is restricted to QUANTIZEDQUANTIZED energy energy state (quanta = bundles of energy)state (quanta = bundles of energy)

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Schrodinger applied idea of e- Schrodinger applied idea of e- behaving as a wave to the behaving as a wave to the problem of electrons in atoms.problem of electrons in atoms.

He developed the He developed the WAVE WAVE EQUATIONEQUATION

Solution gives set of math Solution gives set of math expressions called expressions called WAVE WAVE FUNCTIONS, FUNCTIONS,

Each describes an allowed energy Each describes an allowed energy state of an e-state of an e-

E. SchrodingerE. Schrodinger1887-19611887-1961

Quantum or Wave Quantum or Wave MechanicsMechanics

Quantum or Wave Quantum or Wave MechanicsMechanics

22Heisenberg Heisenberg Uncertainty PrincipleUncertainty Principle

Problem of defining nature Problem of defining nature of electrons in atoms of electrons in atoms solved by W. Heisenberg.solved by W. Heisenberg.

Cannot simultaneously Cannot simultaneously define the position and define the position and momentum (= m•v) of an momentum (= m•v) of an electron.electron.

We define e- energy exactly We define e- energy exactly but accept limitation that but accept limitation that we do not know exact we do not know exact position.position.

Problem of defining nature Problem of defining nature of electrons in atoms of electrons in atoms solved by W. Heisenberg.solved by W. Heisenberg.

Cannot simultaneously Cannot simultaneously define the position and define the position and momentum (= m•v) of an momentum (= m•v) of an electron.electron.

We define e- energy exactly We define e- energy exactly but accept limitation that but accept limitation that we do not know exact we do not know exact position.position.

W. HeisenbergW. Heisenberg1901-19761901-1976