Electrons & Light

Electromagnetic Spectrum : 

Electromagnetic Spectrum Energy can be supplied to electrons in an atom by electromagnetic (or radiant) energy Electromagnetic (radiant) energy travels: In waves Through empty space At the speed of light

Types of Electromagnetic Radiation : 

Types of Electromagnetic Radiation Radio waves Microwaves Radiant heat (infrared) Visible light Ultraviolet (UV), X-rays, Gamma rays All of these combined create the Electromagnetic Spectrum

Properties of a Wave : 

Properties of a Wave Wavelength (l) – distance between 2 peaks or 2 troughs Frequency (n) – number of waves in a given time period (usually 1/sec, or Hz)

Electrons & Light : 

Electrons & Light EM Spectrum & Electrons are related by: Energy of motion of electrons Energy of light Pass current through an element  only certain frequencies of light produced Why are only certain frequencies of light given off? Only absorb enough to move to a specific higher energy level Only emit enough to move to a specific lower energy level

Slide 5: 

Because electrons only have a certain amount of energy Electrons can only orbit at certain distances from the nucleus Energy Levels

Planck’s Hypothesis and Bohr’s Model : 

Energy is given off in little packets called quanta (or photons) Electrons can only absorb or emit photons in whole numbers Electrons can only transfer between orbits whose energy difference equaled the energy absorbed Planck’s Hypothesis and Bohr’s Model

Electromagnetic Waves:Properties & Relationships : 

Electromagnetic Waves:Properties & Relationships Wavelength and frequency are inversely proportional Product of wavelength & frequency produces a constant value Frequency and energy are directly proportional Quotient of energy & frequency produces a constant value Two useful equations derived from these relationships: c (speed of light) 3.0×108 m/s h (Planck’s Constant) 6.626×10-34 Js

Practice : 

Practice If the frequency of a wave is 5.0 x 107 Hz, what is the wavelength?

Practice : 

Practice If the wavelength of a wave is 2.34 x 10-11 m, what is the frequency?

Practice : 

Practice If the frequency of a wave is 3.54 x 108 Hz, what is the energy of the wave?

Practice : 

Practice If the energy of a wave is 45,000 J, what is the frequency of the wave?

Spectroscopy : 

Spectroscopy When atoms are exposed to energy, they absorb some of it to become excited Spectroscopy – method of studying substances being excited by energy Spectrum – pattern of radiant energy studied in spectroscopy

Elemental Fingerprints : 

Elemental Fingerprints Excited atoms relax (eventually) They release energy of a certain frequency When these certain frequencies appear in a spectrum as lines, it is known as an emission spectrum.