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Quantum Mechanical Atom Part I Electromagnetic

Radiation Chapter 8 Section 1 2 of Jespersen

6th ed)

- Dr. C. Yau
- Spring 2013

Electromagnetic Radiation

- Electromagnetic radiation carries E thru space by

means of a wave. - Properties of a wave (Refer to lec. Notes)
- Wavelength (?, pronounced lambda)
- Frequency (?, pronounced nu)
- Amplitude (A)
- Energy of the photon (uniform packets of E,

proportional to frequency)

Units of Measurement

- Wavelength m, cm, ?m, nm,
- angstrom Å
- 1 nm 10 Å
- 1 m 1010 Å
- Frequency cycles per second 1/sec sec-1
- 1 Hertz 1 Hz 1 sec-1
- Energy J, kJ, ergs

How are they related?

? x ? c 2.998x108 m s-1 (speed of light) ? is

inversely proportional to ? Example 8.1 p.

253 Mycobacterium tuberculosis, the organism that

causes tuberculosis, can be completely destroyed

by irradiation with UV light with a wavelength of

254 nm. What is the frequency of this radiation?

Example 8.2 p. 308

Radio station WKXR is an AM radio station

broadcasting from Asheboro, N Carolina, at a

frequency of 1260 kHz. What is the wavelength of

these radio waves expressed in meters? Do

Pract Exer 1, 2, 3 p.308

Energy of a Light Wave

- The energy carried by a light wave is said to be

in discrete packets called "photons." - Size of energy of the photons is proportional to

the frequency of the wave. - E h ?
- where h Planck's constant
- 6.626x10-34 J s
- You dont need to memorize constants.

Relationship between wavelength, frequency

energy of the photon

The Rainbow

- The rainbow is a small region of the

electromagnetic radiation spectrum, the visible

region of the spectrum. - You should know the names of the rest of the

regions of the spectrum, and in order of energy,

frequency and wavelength. (See lecture notes.)

Electromagnetic Radiation Spectrum

- Fig. 8.3 p. 310

Absorption of light by chlorophyll

What is the energy of a photon of the red light

at 700. nm?

- What do we know about energy and the wave?
- How is wavelength related to frequency?
- How is energy related to wavelength?

Continuous vs. Line Spectrum

- What do we see if ordinary white light is passed

through a prism? - If we pass a current through a partially

evacuated tube of a gas, a light is emitted. - If this emitted light is passed through a prism,

we do not see a continuous rainbow, instead we

see...

Figure 8.7 p. 314 Emission Line Spectrum

We see discrete colored lines on a black

background

Line Spectra are like fingerprints

Line Spectrum of H2

- A mathematician came up with an equation that

describes the pattern of lines observed for

hydrogen (the Rydberg Eqn). - The equation does not EXPLAIN why there is such a

pattern. - Bohr came up with his Planetary Model of the Atom

that EXPLAINS why hydrogen would produce such a

pattern of lines. - (See lecture notes.)

Bohr's Calculations

- Each emission line of hydrogen is due to the

energy released in the transition of an electron

from a higher E level to a lower one. - Bohr's equation En ? B/n2
- Bohr's constant, B 2.180x10-18 J
- This allows us to calculate the E of each level.
- The amount of E released is equal to ?E.
- ?E Ehi Elo
- Once we have calculated ?E, we can determine the

corresponding ? and ?. - (See lecture notes.)

Why Schroedinger has to come up with a different

model

- Bohrs theory could predict emission lines for

one electron system ONLY. - What are one-electron systems?
- How is Schroedingers model different from

Bohrs? - See next PowerPoint.