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Unformatted text preview: CHAPTER 7- Atomic Structure and Periodicity 7.1 Electromagnetic radiation- energy that exhibits wavelike behavior and travels at the speed of light in a vacuum. Wavelength- ( ) distance between crests or troughs Frequency- (v_ number of wave cycles per second that pass a given point in space -there is an inverse relationship between wavelength and frequency v=c [ is in meters, v is cycles per second, and c is the speed of light (2.9979 * 10 8 meters per second)] SAMPLE 7.1 The brilliant red colors seen in fireworks are due to the emission of light with wavelengths around 650 nm when strontium salts such as Sr(NO 3 ) 2 and SrCO 3 are heated. (This can be easily demonstrated in the lab by dissolving one of these salts in methaonol that contains a little water and igniting the mixture in an evaporating dish.) Calculate the frequency of red light of wavelength 6.50 * 10 2 nm Answer: 6.5 * 10 2 nm x (1m)/10 9 nm) 6.50 * 10-7 m And v=c/ , so (2.9979 * 10 8 m/s) /(6.50 * 10-7 m) = 4.61 * 10 14 Hz. 7.2 The Nature of Matter-energy can be gained or lost in integer multiples of hv. E= nhv [n = an integer, h= Plank&s constant(6.626 * 10 34 J*s), and v =frequency] -Energy is quantized and can only occur in discrete units of size hv (packets of energy called quanta) SAMPLE 7.2 The blue color in fireworks is often achieved by heating copper(I) chloride(CuCl) to about 1200 C. Then the compound emits blue light having a wavelength of 450 nm. What is the increment of energy (the quantum) that is emitted at 4.50 * 10 2 nm by CuCl? Answer: -v=c/ , so (2.9979 * 10 8 m/s)/(4.50 * 10-7 m) = 6.66 * 10 14 s-1 . And E=hv=(6.626 * 10-34 J*s)(6.66 * 10 14 s-1 ) =4.41* 10-19 J. -EMR can be viewed as a stream of particles called photons E photon = hv= (hc) / -Einstein&s special theory of relativity, E= mc 2 m= E/c 2 and E photon = hc/ , so m = (hc/ )/c 2 = h/(c ) -EMR seems to have characteristics that of waves and particles and this phenomenon is sometimes referred to as the dual nature of light -matter can exhibit wavelike properties de Broglie equation m = h/c = h/v , so = h/mv SAMPLE 7.3 -diffraction- results when light is scattered from a regular array of points or lines - constructive interference- (in phase) peaks of one wave match the peaks of...
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