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wavelength. Visible light. Amplitude. wavelength. Node. Ultraviolet radiation. Electromagnetic Radiation. Figure 7.1. Wave motion: wave length and nodes. Short wavelength --> high frequency high energy. Long wavelength --> small frequency low energy.
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wavelength Visible light Amplitude wavelength Node Ultraviolet radiation Electromagnetic Radiation
Short wavelength --> high frequency high energy Long wavelength --> small frequency low energy
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 • What is the energy of a WONY photon?
Energy of Radiation What is the energy of 1 mole of UV light with wavelength = 230 nm?
Energy of Radiation What is the energy of 1 mole of IR light with wavelength = 1200 nm?
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
Line Emission Spectra of Excited Atoms • Excited atoms emit light of only certain wavelengths • The wavelengths of emitted light depend on the element.
Line Emission Spectra of Excited H Atoms High E Short High Low E Long Low
Origin of Line Spectra Balmer series
For H, the energy levels correspond to: Constant = 2.18 x 10-18 J
Each line corresponds to a transition: Example: n=3 n = 2
Name: ____________ • _________ • _________ • _________ • _________
Quiz Q1. Emission line with longest wavelength Q2. Absorption line with highest frequency Q3. Emission line with lowest frequency Q4. Transition that leads to forming H+
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: • 2 describes 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 p = 3 d = 5 f = 7