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Chapter 5

Chapter 5. Electronic Structure. Light Through a Prism. White light (sunlight) is a blend of all colors (ROY G BIV). combined together. The wavelength ( λ ) and frequency ( υ ) for each color are unique to. that color. As light passes through a prism….

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Chapter 5

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  1. Chapter 5 Electronic Structure

  2. Light Through a Prism • White light (sunlight) is a blend of all colors (ROY G BIV) combined together. • The wavelength (λ) and frequency (υ) for each color are unique to that color. • As light passes through a prism… - the different wavelengths of the colors are separated. - individual colors can be detected by the eye. - a rainbow appears.

  3. The Electromagnetic Spectrum • All substances (radioactive or not) emit electromagnetic radiation. • Only part of the spectrum that human eyes can detect is visible light: (ROYGBIV) • All other radiations have wavelengths that are either too long or too short for our eyes to detect. • The Electromagnetic Spectrum (EM spectrum) is made of the different forms of electromagnetic waves and is based on the frequency and wavelength of the wave. EM waves do not require a medium to travel…..

  4. Cosmic rays Microwaves too short to see too long to see 7.4 x 10-6 m 4.2 x 10-6 m shortest longest Increasing danger

  5. The followinglist [A to G] names the forms of the EM spectrumin order of energy, frequency and wavelength. [A…..largest wavelength, lowest frequency & lowest energy]A . radio waves (includes AM, FM, TV, radar, shortwaves)used for communicationB. microwaves -- used in cooking; can penetrate air, glass, paper and plastic

  6. C. infrared(heating lamps)felt as warmth; used to keep food warmD. visible (only portion that humans can see; smallest part of the spectrum)ROY G. BIV…violet has the greatest energy, frequency, and smallest wavelength of all the colorsE. ultraviolet (causes sunburn)

  7. x-rays (medical use)will pass through the human body with the exception of some bones and tissues • G. gamma rays (treatment of cancer ) can kill living cells • [G…..smallest wavelength, highest frequency & highest energy]

  8. Wavelength vs. Frequency • Wavelength (λ): distance b/n crests of a wave. long wavelength crest Wavelength Wavelength trough short wavelength

  9. Frequency (ν): # of wavelengths that pass a certain point in a given amount of time. - units are Hertz (Hz) • These 2 waves are traveling at = speeds… which wave will have more crests cross the ‘finish line’ in a matter of one min.? low frequency = long wavelength FINISH high frequency = short wavelength *** higher frequency = higher energy ***

  10. Wave Calculations • all waves on the EM spectrum travel at the speed of light (c). • wavelength (λ) and frequency (υ) are inversely related. c = λ(ν) ν ν λ λ • c = speed of light = 3.00 x 108 m/s. • to solve for λ … c = λ ν • to solve for υ … c ν = λ

  11. Practice… Calculate the υ of a wave that has a wavelength of 5.00 x 10-6 m. c 3.00 x 108 ν = ν = ν = 6.00 x 1013 Hz λ 5.00 x 10-6 What is the λ of radiation with a frequency of 1.50 x 1013 Hz? 3.00 x 108 c λ = = λ 2.00 x 10-5 m = λ ν 1.50 x 1013 Does this radiation have a shorter or longer λ than red light? longer …red light ~ 7.4 x 10-6 m

  12. 3.31 x 10-18 J • Max Planck explained that light is emitted in packets (quanta) called ‘photons’ which are distinct bundles of energy. • Planck also assumed that energy of a photon is directly proportional to the frequency of the light. E = h(ν) E ν = h h h • E = energy (in Joules) • υ = frequency • h = Planck’s constant (6.626 x 10-34 J/Hz) • Practice… • Calculate the energy of radiation with a υ of 5.00 x 1015 Hz. E = h(ν) E = 6.626 x 10-34 (5.00 x 1015) E =

  13. Obj. 5…Atomic Spectra • all elements will emit light when excited (i.e. by electricity). • atoms absorb energy and then emit an = amount of energy in the form of light. - atoms emit a characteristic color - Ne = orange - red - Na = bright yellow • if we pass this light through a prism (separate the λ) we get an atomic emission spectrum. ex. of wavelengths emitted set-up

  14. Obj. 5 cont… • emission spectra are unique to particular elements. • only show certain lines of the continuous spectrum (white light). • have helped us gather a lot of info. about our universe! • atomic absorption spectra shows colors missing from the continuous spectrum (missing λ were absorbed by the element). continuous absorption emission

  15. Obj. 6-7…How Atoms Absorb and Emit Energy • e- are found on certain energy levels (orbitals) around the atom. - there is a maximum of seven energy levels in an atom. - e- on the energy level closest to the nucleus have the lowest energy. The 7th energy level has the highest energy. - an e- requires one ‘quanta’ of energy to jump to the next energy level. • e- at their lowest energy level are considered to be at the ground state (most stable). • if e- absorb a quantum or more of energy (from electricity), they can jump to higher energy levels (excited state). • e- must lose energy in order to fall from the excited state back to the ground state. - this energy is emitted in the form of visible light!

  16. Obj. 6-7 cont… • ‘Heinsburg’s uncertainty principle’ states that it is impossible to know exactly where an e- is, b/c it is constantly in motion.

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