1. Electromagnetic Radiation
Foothill Chemistry

2. Electromagnetic Radiation
Form of energy that exhibits wavelike behavior as it travels through space.
Visible Light
X-Rays
Ultraviolet Light
Infrared Light
Radiowaves
Electromagnetic Spectrum – All the forms of EM Radiation

3. Electromagnetic Spectrum

4. Wave Features
Wavelength – The distance between corresponding points on adjacent waves. (Usually measurements are taken peak to peak or trough to trough) – λ (distance measurement – m, cm, nm)
Frequency – The number of waves that pass a given point in a specific time – ν (Hz, s-1)
Speed – Combination of these two = m/s
Amplitude – Height of the Wave

5. Speed of Light c = λν c is the speed of light in m/s
Speed of light is a constant 2.99 x 108 m/s

6. Photoelectric Effect
Emission of electrons from a metal when light shines on the metal.
Doesn’t emit electrons with any light wave, has to have a minimum frequency for the photoelectric effect to occur.
Led to the theory that light is both a wave and a particle

7. Particle Description of Light
Max Planck – EM energy is not emitted continuously, but in packets of energy (quanta).
Quantum of Energy – The minimum quantity of energy that can be lost or gained by an atom
Energy is measured in Joules (J)
E = hν
Planck’s constant = h = x Js

8. Photon Einstein – Light can be thought of as a stream of particles
Photon – Particle of electromagnetic radiation with zero mass and carrying a quantum of energy
Ephoton = hν
Photons are measured in whole numbers

9. Line Emission Spectrum
Ground State - Lowest energy state of an atom
Excited State – State in which atom has a higher potential energy than the ground state
Line Emission Spectrum – The pattern of dark lines and colors made when electromagnetic energy, such as light, passes through a substance and excites its atoms. The excited atoms give off energy in the form of light. Because each type of atom gives off light having a unique range of colors, the emission spectrum can be used to determine the substance’s chemical composition.

10. Line Emission Spectrum

11. Photon Emission
When an excited atom falls from a higher energy state to a lower energy state (or to ground state), a photon of energy is emitted.
E2-E1 = Ephoton = hν
E2 = higher excited state
E1 = lower energy-excited state

12. Photon Emission and Absorption