Electromagnetic Radiation in Quantum Physics
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Explore the properties of electromagnetic radiation, wavelengths, frequencies, and energy levels in quantum mechanics. Learn about photons, quantization of energy, matter waves, and atomic spectra.
Electromagnetic Radiation in Quantum Physics
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wavelength Visible light Amplitude wavelength Node Ultraviolet radiation Chapter 6: Electromagnetic Radiation
Rank the following in order of increasing frequency: microwaves radiowaves X-rays blue light red light UV light IR light
Waves have a frequency • Use the Greek letter “nu”, , for frequency, and units are “cycles per sec” • All radiation: • = c • c = velocity of light = 3.00 x 108 m/sec • Long wavelength --> small frequency • Short wavelength --> high frequency
What is the wavelength of WONY? What is the wavelength of cell phone radiation? Frequency = 850 MHz What is the wavelength of a microwave oven? Frequency = 2.45 GHz
Quantization of Energy Light acts as if it consists of particles called PHOTONS,with discrete energy. Energy of radiation is proportional to frequency E = h • h = Planck’s constant = 6.6262 x 10-34 J•s
E = h • Relationships:
Rank the following in order of increasing photon energy: microwaves radiowaves X-rays blue light red light UV light IR light
E = h • n What is the energy of a WONY photon?
Energy of Radiation What is the frequency of UV light with a wavelength of 230 nm? What is the energy of 1 photon of UV light with wavelength = 230 nm?
What is the energy of a mole of 230 nm photons? Can this light break C-C bonds with an energy of 346 kJ/mol?
Where does light come from? • Excited solids emit a continuous spectrum of light • Excited gas-phase atoms emit only specific wavelengths of light (“lines”)
The Bohr Model of Hydrogen Atom • Light absorbed or emitted is from electrons moving between energy levels • Only certain energies are observed • Therefore, only certain energy levels exist • This is the Quanitization of energy levels
Emission spectra of gaseous atoms • Excited atoms emit light of only certain wavelengths • The wavelengths of emitted light depend on the element.
Constant = 2.18 x 10-18 J For H, the energy levels correspond to: Energy level diagram:
Each line corresponds to a transition: Example: n=3 n = 2
Explanation of line spectra Balmer series
Matter Waves • All matter acts as particles and as waves. • Macroscopic objects have tiny waves- not observed. • For electrons in atoms, wave properties are important. • deBroglie Equation:
Matter waves Macroscopic object: 200 g rock travelling at 20 m/s has a wavelength: Electron inside an atom, moving at 40% of the speed of light:
Heisenberg Uncertainty Principle • Can’t know both the exact location and energy of a particle • So, for electrons, we DO know the energy well, so we don’t know the location well
Schrodinger’s Model of H • Electrons act as standing waves • Certain wave functions are “allowed” • Wave behavior is described by wave functions: • 2describes the probability of finding the electron in a certain spot • Also described as electron density
Example Wavefunction Equation slightly simplified:
It’s all about orbitals • Each wavefunction describes a shape the electron can take, called an ORBITAL • Allowed orbitals are organized by shells and subshells • Shells define size and energy (n = 1, 2, 3, …) • Subshells define shape (s, p, d, f, …) • Number of orbitals is different for each subshell: s = 1 orbital p = 3 orbitals d = 5 orbitals f = 7 orbitals
Which subshell does not exist? • 5s • 2p • 2d • 4f • 15s
NODES Spherical Nodes
