Essay on 06 Lecture CHEM 1211K Subhash

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Chapter 6
Electronic Structure of Atoms

Dr. Subhash C. Goel
South GA College
Douglas, GA
Electronic
Structure of Atoms

A wave is a continuously repeating change or oscillation in matter or in a physical field.
Light is an electromagnetic wave, consisting of oscillations in electric and magnetic fields traveling through space.

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A wave can be characterized by its wavelength and frequency.
Wavelength, symbolized by the Greek letter lambda, , is the distance between any two identical points on adjacent waves.

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Frequency, symbolized by the Greek letter nu, , is the number of wavelengths that pass a fixed point in one unit of time (usually a second). The unit is 1/S or s-1, which is also called the Hertz (Hz).

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Wavelength and frequency are related by the wave speed. The speed of light, c, is 3.00 x 108 m/s. c = 
The relationship between wavelength and frequency due to the constant velocity of light is illustrated on the next slide.

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When the wavelength is reduced by a factor of two, the frequency increases by a factor of two. Copyright © Cengage Learning. All rights reserved.

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Exercise:
1. What is the wavelength of blue light with a frequency of 6.4  1014/s?
2. What is the frequency of light having a wavelength of 681 nm?

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The range of frequencies and wavelengths of electromagnetic radiation is called the electromagnetic spectrum.

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The Nature of Energy
The wave nature of light does not explain how an object can glow when its temperature increases. Also, The wave theory could not explain the photoelectric effect.

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Electronic
Structure
of Atoms

The Nature of Energy

Max Planck explained it by assuming that energy comes in packets called quanta.
© 2012 Pearson Education, Inc.

Electronic
Structure
of Atoms

The Nature of Energy
• Einstein used this assumption to explain the photoelectric effect.
• He concluded that energy is proportional to frequency:
E = h where h is Planck’s constant, 6.626  10−34 J-s.
© 2012 Pearson Education, Inc.

Electronic
Structure
of Atoms

The Nature of Energy
• Therefore, if one knows the wavelength of light, one can calculate the energy in one photon, or packet, of that light: c = 
E = h

© 2012 Pearson Education, Inc.

Electronic
Structure
of Atoms

Exercise Energy of a Photon

Calculate the energy of one photon of yellow light that has a wavelength of 589 nm.

Chemistry, The Central Science, 12th Edition
Theodore L. Brown; H. Eugene LeMay, Jr.; Bruce E. Bursten; Catherine J. Murphy; and Patrick Woodward

© 2012 Pearson Education, Inc.

In the early 1900s, the atom was understood to consist of a positive nucleus around which electrons move (Rutherford’s model).
This explanation left a theoretical dilemma:
According to the physics of the time, an electrically charged particle circling a center would continually lose energy as electromagnetic radiation. But this is not the case—atoms are stable.

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In addition, this understanding could not explain the observation of line spectra of atoms.
A continuous spectrum contains all wavelengths of light.
A line spectrum shows only certain colors or specific wavelengths of light. When atoms are heated, they emit light. This process produces a line spectrum that is specific to that atom. The emission spectra of six elements are shown on the next slide.
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Emission of Energy
(2 Possibilities)

or

Continuous Energy Loss

Electronic
Quantized Energy Loss
Structure
of Atoms

Emission of Energy