The Visible Spectrum 400nm 500nm 600nm 700nm Wavelength means COLOR
Frequency Number of complete events occurring in a period of time Waves/second Examples Second hand on a clock? 1 cycle/minute = 1/60 cycle/sec US Presidential Electons 1 election/4 years = 1/4 election/year
Frequency and Period Period = 1 Frequency
Speed, Wavelength, Frequency c = f
Photon Energy E f E = hf
Properties of Light Speed (c) Nothing travels faster Absolute constant Wavelength ( ) Gamma rays, X-rays, UV, Visible, IR, Radio In visible wavelength means color Frequency (f) Number of complete waves per second Energy of a Photon (E) E = hf
Mercury near Horizon The atmosphere can act like a prism
Continuous Spectrum Source must be HOT and DENSE
Emisson (Bright Line) Spectrum Source must be HOT and TENUOUS
Types of Spectra Continuous Emission Absorption
Rutherford Scattering Experiments Atom He “bullet”
Hydrogen Atoms Simplest atom One proton, one electron Most abundant atom 90% of universe is hydrogen
Planetary Model Force p e-e- Since electron orbits the proton, a force exists.
Planetary Model p e-e- Acceleration Force implies acceleration Accelerating charges emit light Light carries energy (E = hf)
Planetary Model p e-e- Electron moves closer to the nucleus since it requires less energy to be there.
Planetary Model But the electron is still accelerating Must still be radiating energy (light) Must move still closer to the nucleus Electron will spiral into and collide with the nucleus (in about seconds) Atoms do not exist!!
Bohr’s Hypotheses Stable electron orbits exist where the electron does not lose energy.
Electrons can be here or here but not here p
Bohr’s Hypotheses Transitions can occur between orbits so long as the electron ends up with the energy of the new level.
Emission and Absorption Lines Lines come from electron transitions Energy change either comes from (absorption) or is given to (emission) photon. E Photon energy Frequency E = hf Frequency 1/(Wavelength) f = c/ Wavelength means COLOR