1. Quantized Energy and Photons
Section 6.2
Quantized Energy and Photons

2. Objectives Compare the wave and particle models of light.
Define a quantum of energy and explain how it is related to an energy change of matter.
Contrast continuous electromagnetic spectra and atomic emission spectra.

3. Key Terms
Quantum
Plank’s Constant
Photoelectric effect

4. More Than Just a Wave Wave model fails to explain several phenomena:
Blackbody radiation
Photoelectric effect
Emission spectra

5. Hot Objects Heated solids emit radiation Red stovetop White light bulb
Wavelength theories did not explain relationship between intensity and temperature
Blackbody radiation
Emission of light from hot objects

6. Particle Nature of Light
Besides having wave characteristics, light also acts like a particle.
The Quantum Concept: Energy can only be gained or lost in a specified amount  A Quantum.
Equantum = hv
h is Plank’s Constant = x J•s

7. Blocks and Quanta
Think of energy transfer like building a wall of Legos®.
I can only add or take away 1 Lego.
There is no such thing as a ½ Lego.

8. Particle Nature of Light
Photoelectric Effect (Einstein):
electrons, called photoelectrons, are emitted from a metal’s surface when light of a certain frequency shines on the surface.
Photoelectrons
Light

9. The Photon Photon: particle of electromagnetic radiation no mass
carries a quantum of energy
Ephoton = hv

10. Quantized Radiant Energy
Photon strikes and is absorbed by metal surface
Photon transfers energy to an electron in the metal
Amount of energy (work function) is required to overcome the attractive forces (electron & metal)
If photons energy is < that of work function THAN electrons do not escape
If photons energy is > that of work function THAN electrons are emitted
Excess energy appears as kinetic energy of the electrons

11. Atomic Emission Spectra
Electricity passed through a tube of gas
Gas atoms absorb energy and become excited
Atoms release the energy absorbed in the form of light.
Each atom has specific frequencies it will release in the light form.

12. Atomic Emission Spectra
Hydrogen (H)
Helium (He)
Oxygen (O)

13. Atomic Emission Spectra
Neon (Ne)
Xenon (Xe)

14. Neon Signs

15. Homework
on page 253