2. What do you see? Old woman? Or young girl?

3.  Is turning a light on and off a chemical or physical change? ◦ Physical change  What creates light?

4.  Bohr Model – electrons are found in nrg levels UV Light Visible Light Infrared Light

6.  1913, looked at a hydrogen atom  Suggested an e- could move between nrg levels if discrete photons or nrg (amounts of nrg) were absorbed or emitted by the e-  e- falls from high  low nrg = photon emission ◦ Photon has a frequency, or color, that matches the e- fall

7.  When an electron moves from an excited state to its ground state, light nrg is given off. ◦ Excited atom~ e- not in lowest possible nrg state  They have absorbed nrg and jumped to a further nrg level  The color of the light depends on the amount of nrg.  The more nrg levels jumped, the greater the nrg of light.

8.  e- at higher nrg states are not stable  These e- want to return to their ground state to become stable ◦ Lowest possible nrg level  Distance between nrg levels is NOT all the same.

9. R O Y G B I V  Blue light has a higher frequency than red.

10.  Frequency – the # of wave cycles passing a point in a period of time.  As frequency increases, wavelength decreases.

11.  Planck assumed energy can be released and absorbed in discrete packets called quanta.  The energy of one quanta is: Where, known as Planck’s constant.

12.  Light of a particular wavelength (λ) has a particular frequency (ν) and nrg (E).  If ν, λ or E are known, the other 2 can be calculated. speed of light Planck’s constant

13.  Yellow light given off by a sodium vapor lamp has a wavelength of 589 nm. What is the frequency of this radiation?

14.  Unit for frequency (ν) ◦ Hertz  Unit for wavelength (λ) ◦ Meter (m) or nanometer (nm)  Unit for energy (E) ◦ Joule ( J )

15.  Calculate the energy of one photon of yellow light whose wavelength is 589nm.

16.  What do the following symbols stand for? What are their units?  ν  λ  h  c  E Frequency Wavelength Planck’s Constant Speed of Light Energy

17.  Light’s wave nature is seen as its ability to diffract, reflect, refract.

18.  Planck stated that nrg is radiated in discrete packets called quanta.  A photon is a quantum of light having the energy  Light’s particle nature is seen by the emission spectra of elements.

20.  Why each element produces a unique line spectra.

22.  Eventually leads to a very famous equation by a very famous scientist.