Quantized Energy and Photons Section 6.2 Quantized Energy and Photons

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.

Key Terms Quantum Planck’s Constant Photoelectric effect

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

Phenomenon #1

Blackbody radiation (Planck) Heated solids emit radiation Red stovetop White light bulb Wave theories did not explain relationship between temperature and wavelengths

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 Planck’s Constant = 6.626 x 10-34 J•s

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

Phenomenon #2

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

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

Phenomenon #3

Line Spectra (Bohr) 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.

Line Spectra Hydrogen (H) Helium (He) Oxygen (O) http://astro.u-strasbg.fr/~koppen/discharge/index.html

Line Spectra Neon (Ne) Xenon (Xe) http://astro.u-strasbg.fr/~koppen/discharge/index.html

Neon Signs

Assignment Particle Nature of Light Worksheet