Light as a Wave

• Waves are traveling disturbances that carry energy from one place to another

• The speed of a wave is calculated by using the equation:

V = f · λ

Speed = frequency x wavelength

Light as a Wave

• The speed of light is always 3 x 108 m/s

• 300,000,000 m/s• This means that

frequency and wavelength of light waves have an inverse relationship.

[http://www.cartoonstock.com/newscartoons/cartoonists/dbr/lowres/dbrn264l.jpg]

[http://www.andor.com/image_lib/lores/introduction/introduction%20(light)/intlight%201%20small.jpg]

Light as a Wave

Light as a Particle

• Planck’s Theory• Energy that is

absorbed or emitted by an object is restricted to “pieces” (quanta) of energy.

[http://www.dupre-vermiculite.co.uk/images/refractory.jpg]

Light as a Particle

• Planck’s Equation:

E = h · v

Energy = Planck’s Constant x frequency

Planck’s Constant = 6.6261 x 10-34 J-s

Light as a Particle

• Photoelectric Effect• Some colors of

light can cause electrons to eject from the surface of metals.

• Einstein - light exists as photons that carried energy according to Planck’s equation

[http://hyperphysics.phy-astr.gsu.edu/hbase/imgmod2/pelec.gif]

Light & The Bohr Model• When certain

elements are “burned” or electricity is passed through them they create specific colors.

• Atoms must absorb energy and then release it in the form of light.Click here for a flame test video

[http://scripts.mit.edu/~clubchem/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=135&g2_serialNumber=2&g2_GALLERYSID=2e0697a5786c0e9bad5bb7a61f801208]

Light & The Bohr Model

• When the light from these tests is passed through a spectrum, only certain colors appear in the emission line spectrum.

Light & The Bohr Model

• When electrons absorbed energy they would change “orbits” (n=1 to n=2)

• When the electrons “fell” back to their original orbit, they released the energy as light.

[http://www.chemistrydaily.com/chemistry/upload/thumb/d/de/307px-Bohratommodel.png]

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Light & The Bohr Model

• This only worked for Hydrogen!

• It cannot effectively predict atoms with more electrons.

[http://www.incompetech.com/gallimaufry/signs/bohr.gif]

Click here for more spectra