1. You just got finished with your 20 “Nuggets” of knowledge about people who helped shape atomic theory…
We will go back and talk about the early days of atomic theory soon.
Today, let’s focus on the development of atomic theory in the 1900s and WAVE MECHANICS.

2. In the late 1800’s, scientists noticed that objects glowed at certain colors when heated to high temperatures…
Low temps  Warmer  Higher temps Even hotter
Infrared Yellow glow White glow Bluish glow
(not visible) (molten metal) (light bulb)

3. Waves and Light Notes Add a new scientist to your list:
Scientist #21: Max Plank
– Studied the relationship between heat and the color of light that an object gave off. He noticed that only certain colors were produced.
-- Classical physics could not explain it.

4. Max Plank
Conclusion: Energy does not exist as a continuous stream. Energy exists in small, discrete, definite packets of energy called quanta (1 quantum = 1 “chunk” of energy) This is the beginning of quantum mechanics! Energy = Plank’s Constant (h) x frequency E = h∙√ h = x Joule-sec √ = frequency in 1/sec or Hertz

5. Scientist 22 1905 Albert Einstein
Was doing an experiment with light “sometimes” causing a piece of cesium or sodium metal to produce an electric current.
Conclusion: The energy of the light had to be at a particular level in order for an electron to be released. (All or None).
The “Photoelectric Effect”

6. Albert Einstein
Won a Nobel Prize in Physics for his work on the photoelectric effect.
Discovered a relationship between: electrons, light, frequency, energy, and electricity.
Remember E = h∙√ If frequency is high, then energy of light is high.
Discovered that light also acts like it is a particle: photons. This supported Plank’s quantum theory of light.

7. Group of Scientists for #23
Johann Balmer
Theodore (Teddy) Lyman
Fredrick Paschen
These three studied light as it was given off by hydrogen atoms that were heated.
The light contains a pattern of light called an Atomic Emission Spectrum or Bright Line Spectrum.

8. Emission Spectra The pattern for Helium is below.
A non-colored pattern for Hydrogen is below and at the bottom of page 143 in text.

9. Waves A wave is a method of transmitting energy through a medium.
There are two types of waves
Longitudinal waves
Transverse waves

10. Longitudinal Waves
Examples: sound, slinky, traffic

11. Transverse Waves
Examples: water, light, sine

12. General Properties of Waves
Amplitude – a measure of the intensity of the wave
For sound, amplitude is volume
For light, amplitude is brightness
Wavelength λ (lambda) – the distance between one part of a wave and the exact same part on the next wave
Units can be miles, feet, yards, meters, cm, km, nm, Angstroms (1 x 1010 Å = 1 m)

13. General Properties of Waves
Frequency – √ (nu) – the number of waves generated in a specific amount of time
For sound, frequency is pitch
For light, frequency is color or type of energy
Units are in /sec, sec-1, waves/sec, cycles/sec,
Hertz (Hz)

14. Speed c = λ∙√ λ=c/√ √ =c/λ In general, speed = distance/time
For any wave, there is another formula for speed
Speed = wavelength x frequency
For a light wave, the product of frequency and wavelength always equals a constant (c), the speed of light
c = λ∙√ λ=c/√ √ =c/λ

15. The Speed of Light (use the one to match your units!)
186,000 miles/sec
3.00 x 108 m/sec = 300,000,000 m/s
3.00 x 1010 cm/sec = 30,000,000,000 cm/s
3.00 x 1017 nm/s
3.00 x 1018 Å/sec

16. Relationships between variables
As the wavelength of light increases, its frequency decreases
As the frequency of light increases, its wavelength decreases
As the frequency of light increases, the energy increases

17. The Electromagnetic Spectrum
Light is just one kind of Electromagnetic Radiation.
Electromagnetic Radiation includes these kinds of waves: radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays.

19. Electromagnetic Waves
All of these are forms of energy.
All of these travel in transverse waves.
All of these travel at the same speed….
THE SPEED OF LIGHT (c)

20. Louis de Broglie #25
Asked the question: If waves can have particle properties, can particles have wave properties?
He proposed that ALL MATTER could be viewed as having wave properties: electrons, protons, atoms, marbles, elephants, humans!
de Broglie wavelength = Plank’s constant
momentum
 = h
(we will come back to mv
this later)

21. Scientist #24 1912-1914 Niels Bohr
(Draw the picture that is on the board)

22. Atomic Spectra
Passing electric current through a gas in a neon tube energizes the electrons of the atoms of the gas and causes them to emit light.

23. Atomic Spectra
When atoms absorb energy, electrons move into an excited state.
These electrons then lose energy by emitting a photon when they return to lower energy levels.

24. Atomic Spectra
Each specific frequency of visible light emitted corresponds to a particular color.
Each specific element has a unique emission spectrum that consists of discrete lines. No two elements have the same emission spectrum, so it is kind of like a fingerprint for that element!
This is the fingerprint
for Mercury!

25. Atomic Spectra
Much of our knowledge of the composition of the universe comes from studying the atomic spectra of stars, which are hot glowing bodies of gases.

27. Three Differences Between Ground State and Excited State Electrons
Ground State electrons…are closer to the nucleus than excited state electrons.
Ground State electrons…have less energy than excited state electrons.
Ground State electrons…are more stable than excited state electrons.

28. Why could electrons only exist in certain orbits?
No one could explain why until de Broglie (1924).
De Broglie saw a connection between his theory of wave characteristics of matter and the stable orbits of the Bohr model.
An orbit was only stable if it contained an integral (whole) number of electron wavelengths!
1st orbit: 1
2nd orbit: 2 
3rd orbit: 3 