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wavelength. Visible light. Amplitude. wavelength. Node. Ultraviolet radiation. Chapter 6: Electromagnetic Radiation. Figure 7.1. Short wavelength --> high frequency high energy. Long wavelength --> small frequency low energy. Which has the longest wavelength?. Infrared
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wavelength Visible light Amplitude wavelength Node Ultraviolet radiation Chapter 6: Electromagnetic Radiation
Short wavelength --> high frequency high energy Long wavelength --> small frequency low energy
Which has the longest wavelength? • Infrared • Ultraviolet • X-rays • Radio waves
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:
Short wavelength light has: • High frequency and low energy • High frequency and high energy • Low frequency and low energy • Low frequency and high energy
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 photon of 525 nm light? • 3.79 x 10-19 J • 4.83 x 10-22 J • 3.67 x 1020 J • 8.43 x 1023 J
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.
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
Longest wavelength emission? • 1 • 2 • 3 • 4 • 5
Longest wavelength absorption? • 1 • 2 • 3 • 4 • 5
Lowest energy emission? • 1 • 2 • 3 • 4 • 5
Lowest energy absorption? • 1 • 2 • 3 • 4 • 5
Ionization? • 1 • 2 • 3 • 4 • 5
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:
Where is this function zero or near zero? • When x = 0 • When r = 0 • When r is large
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
NODES Spherical Nodes