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8/8/2019 Ch 28 Powerpoint_1

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Chapter 28

Atomic Physics


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Emission Spectrum of Hydrogen

Experimentally, the wavelengths of hydrogens

spectral lines are described by series such as the

Balmer series:

RH is the Rydberg constant RH = 1.0973732 x 10

7 m-1

n is an integer, n = 1, 2, 3,

!

P 22H

n

1

2

1R

1


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Spectral Lines of Hydrogen

Examples of BalmerSeries spectral lines

n = 3, = 656.3 nm

n = 4, = 486.1 nm


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Examples of Emission

Spectra


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Hg Spectrum Demo


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Bohrs Model for Hydrogen

2

21

2e e

eE KE PE m v k

r! !

2

2

ek eEr

!

And if the force of attraction

provides the centripetal

acceleration, then:


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Bohrs Model for Hydrogen cont.

Then Bohr assumed that the electrons orbitalangular momentum is quantized!

mevrn = nh/2T

with n = 1, 2, 3, The principle quantum number

resulting in only certain orbits allowed.

(h = Plancks constant = 6.626 x 10-34 Js)


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Bohrs Model for Hydrogen cont.

With the result that the

energy of the allowed

orbits are:

En = - 13.6 eV/ n2

rn = n2 a0

with a0=0.0529 nm

The Bohr Radius


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Bohrs Energy Level Diagram

Predictions inexcellent

agreement withexperimental data

for Hydrogen

including for RH.

!

P 22H

n

1

2

1R

1


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Photon Energy

Whenever a transition occurs

between a state, ni to another state,

nf(where ni > nf), a photon is emitted.

The photon has a frequency

f = (Ei Ef)/h and wavelength


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Active Figure 28.6


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Active Figure 28.17

An Ionization Problem


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Characteristic X-Rays

When a metal target isbombarded by high-energy electrons, x-raysare emitted.

The x-ray spectrumtypically consists of abroad continuousspectrum and a series ofsharp lines.


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Wave Mechanics - de Broglie Waves

To quantize angular

momentum, de

Broglie then assumedthat an electron orbit

must contain an

integral number of

electron wavelengths.


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de Broglie Waves cont.

De Broglies approach:

resulted in the same quantization ofangular momentum as Bohr used.

indicated that the wave nature of matterwas central to modeling the behavior ofatomic systems.


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Quantum (wave) mechanics

Better experiments and quantum mechanics have

both led to more quantum numbers:

n the principle quantum number (K, L M .

lthe orbital quantum number (s, p, d, f..

mlthe orbital magnetic quantum number

ms the spin magnetic quantum number

All with rules!


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But, The Pauli Exclusion Principle

states that:

No two electrons in an atom can ever have

the same set of values of the quantum

numbers n, , m , and ms.

That explains the electronic structure of

complex atoms as a succession of filled

energy levels with different quantum

numbers.


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Atomic configuration question

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