Light, Energy, and MoreOctober 23, 2007Chemistry

RecapElectromagnetic SpectrumHigh EnergyLow EnergyWave Nature of Light

Whats Going On Here?

When we heat metal what happens?

Does the wave model of light explain these changes?Does not explain different wavelengths and frequencies at different temperaturesWhat is light?Radiation.what is radiation?Particles or rays of energyWhat is temperature anyways?The measure of the average kinetic energy of the particles in an objectKinetic Energy vs. Potential EnergyToo many questions.

Max Planck (1900)German PhysicistBegan to look for answersMatter can only gain or lose energy in small quantized amountsWhats quantized?

Vocab Word!!!QUANTUMMinimum amount of energy that can be gained or lost by an atomThe emitted light from a glowing metal is a ENERGYthis energy is quantized

If energy is now quantizedhow can we determine the amount of energy of a quantum?What is energy measured in?What are we observing?What happens to the color when we increase the temperature (energy)?Proportional or inversely proportional?Now we need a constantPlancks constant, h=6.626 x 10^-34 J*s

Time to put these words into action!What is the frequency and wavelength electromagnetic radiation that emits 1.68 x 10^-17 J of energy? What type of electromagnetic radiation is this?Wavelength= 1.18 x 10^-8 mUltraviolet radiation

Some questions to answerWhat is the color we see?What happens to the energy of the radiation when we increase the frequency, v, of the radiation emitted?Iron at room tempcolor and E?Iron with a little heatcolor and E?Iron with lots of heatcolor and E?

According to Plancks TheoryIf we have a given v, matter can emit or absorb E only in whole number multiples of hv (1hv, 2hv, 3 hv)Matter can ONLY have specific amounts of energyWall of kids building blocksWe can only add or take away in increments of whole blockswe cannot remove half a block

The Big Mystery of the 1900sThe Photoelectric EffectWhat caused these color changes in metals???

Photoelectric EffectElectrons (photoelectrons) are emitted from a metals surface when a light of a certain frequency shines on the surfaceCertain specific amounts of energy (whats this called???) needed to knock out electrons from metal atoms.

Albert Einstein (1905)Added onto Plancks TheoryCalled the electrons emitted, PHOTONS (the little energy packets Planck called quantums)Now Ephoton = hv

Planck paved the way for the explanation behind the mysteryBut some one else came into the picture

Now light is not just a waveEinsteins Dual Nature of LightParticle and wave characteristicsLight is a beam of tiny particles, called photons, acting like a wave

NEW WORD!!!PhotonA particle of electromagnetic radiation with no mass that carries a quantum of energy

What Einstein addedEnergy of a photon has a minimum or threshold value to eject photoelectronsWhat must happen for the photoelectric effect to occur?Energy of a photon (particle of EM radiation) must have the minimum energy requirement to free the electron from the atom of metal

Mystery Solved!No matter how long a light of a certain frequency is shone on metal (intensity), electrons will not be ejected unless the minimum amount of energy is shone.Silver metalPhotoelectrons ejected when a light with a frequency of at least 1.14 x 10^15 Hz or greater is usedSodium metalRed lightViolet light

Revised Plancks WorkEinstein piggy-backed off of Plancks Theory and we now have..Photon

Time to do a little work.Tiny water drops in the air disperse the white light of the sun into a rainbow. What is the Energy oa a photon from the violet portion of the rainbow if it has a frequency of 7.23x10^14 Hz?E=4.79 x 10^-19 JEnergy in a photon of violet light

A couple more A photon has an energy of 2.93 x 10^-25 J. What is its frequency? What type of electromagnetic radiation is the photon?V=4.42 x 10^8 HzTV or FM waves

Practice makes perfect What is the energy of each photon in the following types of radiation?6.32 x 10^20 Hz9.50 x 10^13 Hz1.05 x 10^16 HzWhat types of radiation are each?4.19 x 10^-13 J gamma or x-ray6.29 x 10^20 J infrared6.96 x 10^-18 J ultraviolet