1. Light and the Atom

2. Light Much of what we know about the atom has been learned through experiments with light; thus, you need to know some fundamental concepts of light in order to understand the structure of the atom, especially the placement of the electrons. Characteristics of Light – –Has "Dual" nature (or split personality) – –There are times in which it behaves like a WAVE and other times when it behaves like a PARTICLE

3. Light as a Wave Electromagnetic Spectrum Electromagnetic Spectrum

4. Wave Calculations c =  λ  C = speed of light (constant 3 x 10 8 m/s) C = speed of light (constant 3 x 10 8 m/s) –ν = Greek letter nu, frequency –λ = Greek letter lambda, wavelength speed of electromagnetic waves is always the same, wavelength and frequency can change and are inversely related speed of electromagnetic waves is always the same, wavelength and frequency can change and are inversely related frequency – number of waves that pass a given point per second frequency – number of waves that pass a given point per second Wavelength – the length of one entire wave Wavelength – the length of one entire wave

5. example The yellow light given off by a sodium vapor lamp used for parking lots has a wavelength of 589 nm. What is the frequency of this radiation? (pay attention to the units) The yellow light given off by a sodium vapor lamp used for parking lots has a wavelength of 589 nm. What is the frequency of this radiation? (pay attention to the units) 5.09 x 10 14 s -1 5.09 x 10 14 s -1

6. Light as a Particle When light behaves as a particle, it is called a PHOTON. We are interested in how much energy they have. The unit of energy we will use is the Joule, J.

7. Max Planck (1900) matter does not gain or lose energy in a continuous manner, but in small, specific amounts (quanta) matter does not gain or lose energy in a continuous manner, but in small, specific amounts (quanta) quantum – minimum amount of energy that can be gained or lost by an atom quantum – minimum amount of energy that can be gained or lost by an atom mathematically demonstrated the relationship between energy of a quantum and emitted radiation mathematically demonstrated the relationship between energy of a quantum and emitted radiation

8. The Energy of Light E = h  Where E = energy h = Planck’s constant (6.626 x 10 -34 Js)  frequency

9. Examples 1. 1.What is the energy of a photon of light whose frequency is 7.85 x 10 15 Hz? 2. 2.If a light has a wavelength of 550 nm, what is the energy of one photon of this light?