EXAM #2 RESULTS THIS WEEK’S SCHEDULE LECTURE- LAB- Announcements

Energy is Quantized Light also acts like particles Photon= “Packet” of energy Energy is proportional to Frequency (and ) Planck’s Equation:

UV-B Light and DNA Damage

Some more examples… How much energy does a mole of 230nm photons possess? Can this light break a C-C bond with an energy of 346kJ/mol?

Does 1 mole of 1200nm photons have enough energy to break a C-C bond? 1. Yes 2. No 3. Abstain

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

Emission spectra of gaseous atoms Excited atoms emit light of only certain wavelengths The wavelengths of emitted light depend on the element.

Absorption and Emission Spectra

Line spectra of atoms

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  Energy levels are Quantized