Presentation on theme: "What do you see? Old woman? Or young girl? Is turning a light on and off a chemical or physical change? ◦ Physical change What creates light?"— Presentation transcript:
What do you see? Old woman? Or young girl?
Is turning a light on and off a chemical or physical change? ◦ Physical change What creates light?
Bohr Model – electrons are found in nrg levels UV Light Visible Light Infrared Light
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
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.
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.
R O Y G B I V Blue light has a higher frequency than red.
Frequency – the # of wave cycles passing a point in a period of time. As frequency increases, wavelength decreases.
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.
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
Yellow light given off by a sodium vapor lamp has a wavelength of 589 nm. What is the frequency of this radiation?
Unit for frequency (ν) ◦ Hertz Unit for wavelength (λ) ◦ Meter (m) or nanometer (nm) Unit for energy (E) ◦ Joule ( J )
Calculate the energy of one photon of yellow light whose wavelength is 589nm.
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
Light’s wave nature is seen as its ability to diffract, reflect, refract.
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.
Why each element produces a unique line spectra.
Eventually leads to a very famous equation by a very famous scientist.