1. 4-2 Quantum Theory

2. Planck’s Theory Max Planck predicted accurately how the spectrum of radiation emitted by an object changes with temperature.

3. Proposed that there is a fundamental restriction on the amounts of energy that an object emits or absorbs, called quantum. –Means FIXED AMOUNTS

4. Completely contradicted the idea that energy can emit or absorb in any amount. Related the Frequency of the radiation to the amount of energy. E = h Energy = Planck’s Constant x Frequency

5. Planck’s Constant (h) = 6.6262 x 10 -34 J-s (Joule x second) Energies absorbed or emitted by atoms are quantized, which means that their values are restricted to certain quantities. Energy is not continuous

6. Example Imagine a car’s fundamental quantum of energy corresponds to a speed of 10 km/hr. If the car has 7 quanta of energy, it will have a speed of 70 km/hr. If the car has 9 quanta of energy, it will have a speed of 90 km/hr. This shows that a car can only move in multiples of 10 km/hr (in this case). Speeds such as 88 km/hr and 41 km/hr are impossible

7. QuantizedContinuous

8. Why can’t we see quantized energy around us? –Planck’s Constant is very small. The Quanta are too small for every day notice, but to a very small atom they make a big difference

9. The Photoelectric Effect In the photoelectric effect, electrons are ejected from the surface of a metal when light shines on it. Einstein realized that Planck’s idea of energy quanta could explain this. Said that Light consists of quanta of energy that behave like tiny particles, called PHOTONS

10. Red light will not cause electrons to flow in a sheet of sodium metal, no matter how long or bright the source is. Violet light will cause electrons to flow. Violet light has a greater frequency, and a greater amount of energy per photon

12. The frequency of light and the energy of the photon explains the effects of electromagnetic radiation. X-rays contain high amounts of energy because of their frequency, while radio waves have low frequency and low energy.

13. Dual Nature of Radiant Energy Arthur Compton later demonstrated that photons can collide with electrons. Photons behave like a particle that always travels at the speed of light. E = mc 2 =h