Modern ChemistryChapter 4

Arrangement of Electrons

in AtomsSections 1-3

The Development of a New Atomic ModelThe Quantum Model of the Atom

Electron Configurations

Section 1

The Development of a New Atomic

Model

Sect

ion 1

Voca

bula

ry Electromagnetic radiationElectromagnetic spectrumWavelengthFrequencyPhotoelectric effectQuantumPhotonGround StateExcited stateLine-emission spectrumContinuous spectrum

Properties of Light• Electromagnetic Radiation: a form

of energy that exhibits wavelike behavior as it travels through space.

• Wavelength: the distance between corresponding points on adjacent waves

• Frequency: the number of waves that pass a given point in a specific time.

Properties of a Wave:Properties of a Wave:

• Amplitude – is the height of the wave Amplitude – is the height of the wave measured from the origin to its crest.measured from the origin to its crest.– The brightness or intensity of the light The brightness or intensity of the light

depends on the amplitude.depends on the amplitude.

– The greater the amplitude, the brighter the The greater the amplitude, the brighter the light.light.

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Electromagnetic Spectrum Image

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Properties of Light• wavelength x frequency = speed of light

• x = c• Visible Light = R O Y G B I V

Long

Low Low E

Short

High High E

The Photoelectric Effect • Max Planck proposed that energy is

proportional to the frequency of the electromagnetic wave.

• Electromagnetic energy is emitted from objects in small packages called quanta.

• E = h •Planck’s constant

–h = 6.626 x 10-34 J•sec

Light as ParticlesLight as Particles

• QuantizedQuantized ContinuousContinuous

Quanit

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The Photoelectric Effect • Albert Einstein expanded on

Planck’s idea.• Electromagnetic radiation has a

dual wave-particle nature.• A particle of light is a photon.• Photon: a particle of

electromagnetic radiation having zero mass and carrying a quantum of energy.

• Ephoton = h

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The Photoelectric Effect• The

photoelectric effect refers to the emission of electrons from a metal when light shines on the metal.

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Photo

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The Photoelectric Effect To knock an electron loose,it must be hit with a photon whichpossesses a minimum amount of energy.This energy corresponds to its frequency.Different metals hold electrons

more or less tightlySo different metals require

different frequencies to show the photoelectric effect.

The H-Atom’s Line Emission Spectrum

• Electric current is passed through a vacuum tube with hydrogen in it.

• A glow is produced• When shined

through a prism a line emission spectrum is produced

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Bohr Model of the Atom • Niels Bohr proposed orbits for the

electrons• Each orbit has a fixed energy• Lower energy orbits are closer to

the nucleus• Between orbits the

electron cannot exist

Explaining the Line Emission Spectrum An electron absorbs a specific amount of

energy (absorption) and moves from its ground state to an excited state

Explaining the Line Emission Spectrum The electron returns to its ground

state and emits a photon (emission).

Explaining the Line Emission Spectrum This photon has an energy corresponding to

the difference between the two states.This photon has a specific E, , and color.

Photo

n E

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Bohr Model of the Atom • Bohr’s calculated values for the

lines agreed with the values observed for the lines in each series.

• However, it did not explain the spectraof atoms with more thanone electron.

Bohr

Mod

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Bohr and Einstein