Unit 3: Light and Electrons

Electromagnetic Radiation Light is electromagnetic radiation: combined electric and magnetic waves Source Electric vector Magnetic vector direction of propagation

Electromagnetic Radiation Light is more than what we can see…

Electromagnetic Radiation Subatomic particles (electron, photon, proton, etc) exhibit both PARTICLE and WAVE properties. This is known as Wave-Particle Duality. Diffraction: wave-like Photoelectric Effect: particle-like

Electromagnetic Radiation Wave Properties of Light: It’s fast! …c = 3.0 x 108 m/s It relfects, refracts, diffracts (Transverse wave)

Electromagnetic Radiation All light waves have frequency wavelength symbol: ν (Greek “nu”) l (Greek “lambda”) units: “cycles per sec” = Hertz “distance” (m, nm) c = l · ν where c = speed of light = 3.00 x 108 m/sec Increasing frequency

Electromagnetic Radiation Example: Red light has l = 700. nm. Calculate the frequency, f. = 3.00 x 10 8 m/s 700. x 10 -9 m 4.29 x 10 14 /s ν = C l

Electromagnetic Radiation Particle Properties of Light: A particle of light is called a photon Energy of a photon is calculated by E = h · ν where E = energy (Joules, J) ν = frequency (Hertz, Hz, 1/sec) h = Planck’s constant 6.63 x 10 J·s -34

Electromagnetic Radiation Albert Einstein postulates the Photoelectric Effect to explain two observations: No electrons are observed until a minimum energy is applied. Number of electrons ejected depends upon light intensity – not light frequency!

Light is created by the Photoelectric Effect

Electromagnetic Radiation The photoelectric effect and the idea of discrete, quantized energies neatly explain the observation of emission spectra.

Electromagnetic Radiation Example: Red light has l = 700. nm. Calculate the energy per photon. E = hν and c = lν So ν = c/l and E = hc/l E = (6.63 x 10 Js)(3.0 x 10 m/s) 700. x 10 m E = 2.84 x 10 J -34 8 -19 -9

Electron Orbitals Electron Orbitals While thinking about the emission spectrum of hydrogen, Neils Bohr came up with the planetary model of the atom. In this model, electrons can only orbit the nucleus at discrete distances and particular orbital shape. Orbital model of Na Sharp-line spectrum of H Neils Bohr