Section 6 2 Quantized Energy and Photons Objectives

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 • Plank’s Constant • Photoelectric effect

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

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

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 = 6. 626 x 10 -34 J • s

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.

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

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

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

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.