1. Niels Bohr’s Energy Levels
Electrons in certain energy levels
Orbits with certain amounts of energy
Low energy levels: closer to nucleus
High energy levels: farther from nucleus
Ground state
Electrons in lowest energy level possible
Aufbau principle
Electrons will occupy the lowest available energy level
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2. Excited Atom Atom has absorbed energy Excited state is unstable
Quanta – Energy required to excite an electron
Excited state is unstable
Atom soon emits same amount of absorbed energy
Energy seen as visible light
Photon – particle with no mass containing a quanta of energy
COLOR
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3. Wave Description of Light
Wavelength (λ)
Distance between corresponding points on adjacent waves
Frequency(f or γ)
The number of waves passing a given point in a given time
Hertz
C = λf
C = 3.0 x 108 m/s : speed of light
Episode 303

4. Electromagnetic Spectrum
What is the frequency of light if the wavelength is 6.0 x 10-7 m?
C = λf
C = 3.0 x 108 m/s : speed of light
3.0 x 108 m/s = (6.0 x10-7 m) f
3.0 x 108 m/s
= f
6.0 x10-7 m
5.0 x 1014/s = f
Episode 303

5. Electromagnetic Spectrum
What is the wavelength of light if its frequency is 5.0 x 1014 Hertz?
C = λf
C = 3.0 x 108 m/s : speed of light
3.0 x 108 m/s = λ(5.0 x 1014/s)
3.0 x 108 m/s
= λ
5.0 x 1014/s
6.0 x 10-7 m = λ
Episode 303

6. Particle Description of Light
Energy exists as particles called quanta
Photoelectric Effect
Metal emits electrons when light strikes the metal
E =hf
h is Plank’s Constant
6.626 x Js
Episode 303

7. Electromagnetic Spectrum
How much energy does light contain if its frequency is 5.0 x 1014 Hertz?
E = hf
h = x Js : Plank’s Constant
E= (6.626 x 10-34Js)(5.0 x 1014/s)
E = 3.3 x J
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8. The Modern View of Light
Light has a dual nature
Light may behave as a wave
Light may behave as a stream of particles called quanta or photons
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9. Spectroscopy
Spectral lines represent energy released as electrons return to lower energy levels
Spectral lines identify an element
Called the Bright Line Spectrum of an Element
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10. Orbital Region of space where an electron is likely to be found
Region of space where an electron is likely to be found
Heisenberg Uncertainty Principle
Impossible to determine location and velocity of a particle
Episode 303