Chapter 07

# Chapter 07 - CHEMISTRY The Molecular Science Chapter Seven...

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CHEMISTRY The Molecular Science Chapter Seven Electron Configurations and the Periodic Table

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Electromagnetic Radiation Consists of electric and magnetic fields oscillating in perpendicular planes. Travel at the same speed in a vacuum, c, speed of light. Electromagnetic wave is described in terms of wavelength – distance between adjacent crests (nm, μm). frequency – number of waves passing a point in a second (s -1 , Hz). amplitude – height of the crest (intensity).
Wavelength –Frequency – Amplitude

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Electromagnetic Spectrum
Frequency is related to wavelength: νλ = c c = speed of light = 2.998x10 8 m/s ν = frequency (s –1 ) λ = wavelength (m) Practice Problem 7.1 p. 275 A laser developed for use with digital video disc (DVD) players has a wavelength of 405 nm. Calculate the frequency of this radiation in hertz (Hz). 1 nm = 1x10 –9 m

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Black Body Radiation − emission spectrum of a heated object. Planck: an atom in a hot object emits light in units of quanta (photons). Light is quantized Quantum Theory. E quantum = hν radiation h = Planck’s constant = 6.626x10 –34 Js
E = hν ν = c/λ E = hc/ λ The energy per quantum (photon) of radiation increases as the wavelength gets shorter. Practice Problem 7.2 p. 277 (Refer to Figure 7.1 p. 274) Which has more energy, a) One quantum of microwave radiation or one quantum of ultraviolet radiation? b) One quantum of blue light or one quantum of green light?

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Photoelectric Effect The emission of electrons by substances, such as metals, when light of a certain wavelength falls on their surfaces . There is a threshold wavelength below which no photoelectric effect is observed, no matter how bright or intense the light is. Different metals require light of different energies to emit electrons. Einstein renamed a quantum = photon. Photons of different λ have different energy. E min = hν is the minimum energy of light to observe emission of electrons.
Photoelectric Effect

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Photons A photon = unit of electromagnetic energy. Photons have both particle and wave properties (dual nature of light. Massless particle behavior – photoelectric effect. Wave behavior – diffraction.
Diffraction patterns – wave nature of light When waves of light pass through adjacent narrow slits, the waves become scattered and spread out. They can interact destructively or constructively to produce dark or light spots.

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If a high voltage is applied to a gaseous element at low pressure, the atoms absorb energy and become excited. The excited atoms then emit the extra energy as radiation. Spectrum – distribution of intensities of wavelengths or frequencies of EM radiation emitted or absorbed by an object. Characteristic of a specific emitting substance.
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## This note was uploaded on 10/03/2010 for the course CHE 131 taught by Professor Kerber during the Summer '08 term at SUNY Stony Brook.

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Chapter 07 - CHEMISTRY The Molecular Science Chapter Seven...

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