Download Electrons in Atoms Section 5.1

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.
Atomic Emission Spectra
Hydrogen (H)
Helium (He)
Oxygen (O)
http://astro.u-strasbg.fr/~koppen/discharge/index.html
Atomic Emission Spectra
Neon (Ne)
Xenon (Xe)
http://astro.u-strasbg.fr/~koppen/discharge/index.html
Neon Signs
Homework
• 6.21-6.28 on page 253