Quantum Theory of the AtomPage 2

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Found that blackbody radiation was quantized.

1900—Nobel Prize in 1918

Slide 9

What is Quantized?

Energy can have only certain values (quantities), not in between, instead of a continuum of values. This is like energy existing on stairs of a staircase instead of at any energy on a ramp.

Slide 10

Presentation of Lecture Outlines, 7–10

Figure 7.2: Emission (line) spectra of some elements.

Slide 11

Quantum Effects and Photons

Presentation of Lecture Outlines, 7–11

E=

ג

hc

h=Planck’s constant 6.626 x 10-34Js c=speed of light 3.00 x 108 m/s ג=wavelength of light

What is the energy of red light? (6.626x10-34Js)(3.00x108m/s) E= (700x10-9m)

E= 2.84 x10-19Joules

Slide 12

Einstein’s Photoelectric Effect (1905--Nobel Prize in 1921)

Only light from a certain color (energy) could eject electrons. Intensity of the light had no effect. Energy is absorbed only at quantized energies!

(Animation of Photoelectron Effect) (Adsorption and Emission Spectra)

Slide 13

Presentation of Lecture Outlines, 7–13

Einstein’s assumption that an electron is ejected when struck by a single photon implies that it behaves like a particle.

Quantum Effects and Photons

Photoelectric Effect

When the photon hits the metal, its energy, hn is taken up by the electron.

The photon ceases to exist as a particle; it is said to be “absorbed.”

Slide 14

Presentation of Lecture Outlines, 7–14

The “wave” and “particle” pictures of light should be regarded as complementary views of the same physical entity.

Quantum Effects and Photons

Photoelectric Effect

This is called the wave-particle duality of light.

The equation E = hn displays this duality; E is the energy of the “particle” photon, and n is the frequency of the associated “wave.”

Slide 15