chapter 7

# chapter 7 - CHAPTER 7 Atomic Structure &amp; Periodicity 1...

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Atomic Structure & Periodicity CHAPTER 7 1

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Theories about energy and arrangement of electrons in atoms are based on experimental studies of the interaction of matter with EM radiation, of which visible light is a familiar form 7.1 Electromagnetic Radiation 2
Matter atoms gain energy by absorbing EM radiation and then release energy by emitting EM radiation Excited state ground state Independence Day fireworks in San Diego, California . - Wikipedia 3

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Electromagnetic radiation and matter microwaves 4
Some definitions…. EM radiation : consists of oscillating perpendicular electric and magnetic fields EM radiation can be described in terms of frequency ( ν ) and wavelength ( λ ) Spectrum is the distribution of intensities of wavelengths or frequencies of EM radiation emitted or absorbed by an object 5

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Amplitude: height of the wave If two EM have same frequency, then they have same wavelength, but may differ in amplitude 6
Number of complete waves passing a point in a given period of time or cycles per second or sec -1 4.80 x 10 14 sec -1 means that 4.80 x 10 14 waves pass a fixed point per second 7

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ν = c/ λ Where c is the speed of light in vacuum c = 2.9979 x 10 8 m/s 8
2.998 x 10 8 m/s Microwaves from a home microwave oven has a frequency of 2.45 x 10 9 s -1 . Calculate the wavelength of this radiation in nanometers. λ = c/ υ λ = 2.45 x 10 9 /s = 1.22 x 10 -1 m = 1.22 x 10 8 nm 9

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Evidence for energy quantization in atoms Max Planck’s blackbody radiation experiment that introduced the concept of energy quantization 7.2 The nature of matter 10
Energy is in fact quantized and can occur only in discrete units of h υ E = h υ radiation = hc/ λ h: plank constant 6.626×10 -34 J·s energy E= 0 E= hv E= 2hv E= 3hv Exercise 7.2 on page 278 11

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Energy of one quantum of orange light will be… υ orange = 4.80 x 10 14 sec -1 Solution: υ orange = 4.80 x 10 14 sec -1 and h = 6.626 x 10 -34 J sec So E orange light = h υ = 31.80 x 10 -20 J 12
Energy per quantum increases as wavelengths get shorter E = hc/ λ or E = h υ 13

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Electrons occupy distinct energy levels within the atom. Einstein’s photoelectric effect Electrons are emitted from the surface of a metal when light strikes it. light Photosensitive metal cathode Electrons bounce off and are attracted to the anode causing an electric current to flow which is read on the ammeter 14
No electrons are emitted by a given metal below a specific threshold frequency υ 0. • Above υ 0 , the numbers of electrons emitted increases with the intensity of the light. • Above υ 0 , the kinetic energy of the emitted electrons increases linearly with the frequency of the light. E

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## chapter 7 - CHAPTER 7 Atomic Structure &amp; Periodicity 1...

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