Long wavelength --> small frequency low energy Short wavelength --> high frequency high energy
Which has the longest wavelength? 1.Infrared 2.Ultraviolet 3.X-rays 4.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 10 8 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
Energy of radiation is proportional to frequency h = Planck’s constant = x Js Light acts as if it consists of particles called PHOTONS, with discrete energy. E = h Quantization of Energy
Relationships: E = h
Short wavelength light has: 1.High frequency and low energy 2.High frequency and high energy 3.Low frequency and low energy 4.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 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? x J x J x J x 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?
Does 1200 nm light have enough energy to break C-C bonds?
Where does light come from? Excited solids emit a continuous spectrum of light Excited gas-phase atoms emit only specific wavelengths of light (“lines”)
Light emitted by solids
Light emitted by hydrogen gas
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
Excited atoms emit light of only certain wavelengths The wavelengths of emitted light depend on the element. Emission spectra of gaseous atoms
Line spectra of atoms
For H, the energy levels correspond to: Constant = 2.18 x J Energy level diagram:
Each line corresponds to a transition: Example: n=3 n = 2
Balmer series Explanation of line spectra
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:
Can see matter waves in experiments
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:
Where is this function zero or near zero? 1.When x = 0 2.When r = 0 3.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