Electromagnetic Spectrum

Quantum Mechanics At the conclusion of our time together, you should be able to:  Define the EMS (electromagnetic spectrum.  List the various parts of a wave of electromagnetic radiation  Explain how this radiation is “quantized” by the electrons in an atom.  Use this information to determine an unknown element with a flame test.

EMS Made up of electromagnetic radiation Form of energy Form of energy Behaves like a wave Behaves like a wave

Kinds of radiation are:  Gamma Rays  X Rays  Ultraviolet Rays  VISIBLE LIGHT  Infrared  Microwave  Radio Waves

Electromagnetic Radiation

Kinds of Radiation are:

Features of Waves Have repetitive motion Have repetitive motion Characterized by four properties: Characterized by four properties:  Wavelength  Frequency  Amplitude  Speed

Wavelength (ג) One full cycle of a wave One full cycle of a wave Crest to Crest or Trough to Trough Crest to Crest or Trough to Trough Wavelengths of visible light are 400 – 750 nanometers Wavelengths of visible light are 400 – 750 nanometers Violet Light = short wavelength Violet Light = short wavelength high frequency high frequency Red Light = long wavelength Red Light = long wavelength low frequency low frequency

Frequency (v) The number of cycles (one upward and downward motion) a wave completes in one second. The number of cycles (one upward and downward motion) a wave completes in one second. Speed of light – is a constant (c) Speed of light – is a constant (c) Speed = 3.0 x 10 8 meters per second (in air) Speed = 3.0 x 10 8 meters per second (in air) Waves travel slower through other types of matter Waves travel slower through other types of matter

Amplitude Height of a wave Height of a wave Measured from origin to peak Measured from origin to peak

Relationship between (ג and v) C = ( ג ) x (v) Where: c = speed of light ג = wavelength v = frequency

Check Out the Following Examples:

Since the speed of light is constant, wavelength & frequency have a constant relationship They are inversely proportional As wavelength of light decreases, the frequency of light increases As wavelength of light increases, the frequency of light decreases

How are Energy & Frequency Related? They are directly proportional They are directly proportional As frequency increases, energy increases As frequency increases, energy increases As frequency decreases, energy decreases As frequency decreases, energy decreases

The Photoelectric Effect Emission of electrons from a metal when light shines on the metal Emission of electrons from a metal when light shines on the metal Wave Theory says that light of any frequency should be capable of supplying enough energy to loosen an electron Wave Theory says that light of any frequency should be capable of supplying enough energy to loosen an electron THIS WAS NOT THE CASE There was a minimum frequency that had to be met before the photoelectric effect would occur There was a minimum frequency that had to be met before the photoelectric effect would occur

Albert Einstein 1905 – “Electromagnetic Radiation has a dual wave – particle existence” 1905 – “Electromagnetic Radiation has a dual wave – particle existence” A particle of electromagnetic radiation (light) with zero mass and a quantum of energy is called a photon A particle of electromagnetic radiation (light) with zero mass and a quantum of energy is called a photon

Hypothesis : Light could be a wave Light could be a wave Light could be a stream of particles Light could be a stream of particles Photon =particle of radiation Photon =particle of radiation has no mass has no mass carries a quantum of energy E photon = (h) x (v) This won Einstein his only Nobel Prize

Photon = a particle of light. Electromagnetic Radiation ALL light. Visible AND Invisible visible light, x-rays, gamma rays, radio waves, microwaves, ultraviolet rays, infrared.

Photon a particle of light Laser

Can electrons act as a particle and a wave??? French Scientist: Louis de Broglie French Scientist: Louis de Broglie Discovered that electrons have a similar amount of energy as a photon Discovered that electrons have a similar amount of energy as a photon

German Physicist Max Planck discovered: Objects emit energy in small, specific amounts called quanta Objects emit energy in small, specific amounts called quanta Quantum – minimum quantity of energy that can be lost or gained by an electron Quantum – minimum quantity of energy that can be lost or gained by an electron (His work proved Einstein correct) E = h * v E = energy h = Planck’s constant (6.626E-34 J*s) v = frequency of radiation

20 th Century Atomic Theory: Atomic Theory: Neils Bohr’s theory involved absorption and emission of light Neils Bohr’s theory involved absorption and emission of light When an electron jumped to a higher energy level, it absorbed energy When an electron jumped to a higher energy level, it absorbed energy When an electron returned to a lower energy level it gave off energy in the form of light When an electron returned to a lower energy level it gave off energy in the form of light

Bohr Model of the Atom When an electron jumps to a higher energy level, it absorbs energy (green arrows). When an electron returns to a lower energy level, it gives off energy in the form of light (purple arrows)

Quantum Mechanics The energy of the particles in the Bohr atom is restricted to certain determined values. It can be said that the energy is quantized; this means that only certain orbits with certain radii exist and any other orbits do not exist.

Quantum Mechanics Let’s see if you can:  Define the EMS (electromagnetic spectrum.  List the various parts of a wave of electromagnetic radiation  Explain how this radiation is “quantized” by the electrons in an atom.  Use this information to determine an unknown element with a flame test.