Electromagnetic Radiation Foothill Chemistry

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

Electromagnetic Spectrum

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

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

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

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 = 6.626 x 10-34 Js

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

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.

Line Emission Spectrum

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

Photon Emission and Absorption