Chapter 7 Electronic Structure of Atoms. The Wave Nature of Light The electronic structure of an...
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Transcript of Chapter 7 Electronic Structure of Atoms. The Wave Nature of Light The electronic structure of an...
Chapter 7
Electronic Structure of Atoms
The Wave Nature of Light
• The electronic structure of an atom refers to the arrangement of the electrons.
• Visible light is a form of Electromagnetic radiation (EMR).
• Radiation carries energy through space• EMR is characterized by its wave
Wave Properties
• All waves have a characteristic wavelength, λ (lambda), and amplitude, A.
• The frequency, ν (nu), of a wave is the number of cycles which pass a point in one second.
• The units of ν are Hertz. (1Hz = 1/s)
• The speed of EMR is always the same no matter what the wavelength or frequency.
• EMR speed is the speed of light.
• c is the symbol for the speed of light
• C = 3.0 x 108m/s
• The relationship between frequency (ν ) and wavelength
(λ )is shown by the equation
c = λ νWhere
c = the speed of light = 3.0 x 108m/s
λ = the wavelength of the wave
ν = the frequency of the wave (Hz)
• Frequency and wavelength are inversely related.
• Since the speed of the wave is constant (3.0 x 108m/s) , if the frequency is known, the wavelength can be determined.
• Likewise, if the wavelength is known, the frequency can be determined.
Light as Electricity and Magnetism
o Max Planck determined mathematically that light is both magnetism and electricity.
o He determined the Energy in a photon is directly related to its frequency .
oIf the frequency is multiplied by Planck’s constant (6.6261 x 10-34 J-s), the Energy of the photon can be determined.
o This relationship is represented in the formula
E=h νWhere E = Energy h = 6.6261 x 10-34 J.s (Planck’s
constant) ν = frequency
How does this relate to atomic models?
Thomson’s Model
Thomson had the Plum Pudding Model.Negative particles interspersed in positive atom, NEUTRALLY CHARGED.
Changed Dalton’s Model:Atom is NOT smallest particle of matter.
•Rutherford’s Model
PROBLEMS•Could not explain the chemical properties of the elements.•Why do metals give off characteristic colors when heated in a flame?•When heated iron glows red, then yellow, then white. WHY?
Dense positive center with electrons outside the nucleus.
BOHR MODELGOAL: To improve Rutherford’s Atomic Model
QUANTUM MECHANICAL MODEL OF THE ATOM
• The quantum mechanical model is a way of describing the atom through electron movement.
• Electrons are arranged in orbitals (path the electron follows) in Energy levels (distance from the nucleus) around the nucleus.
• If the electrons gain a photon (specific amount) of energy they can travel to higher energy levels.
• The energy level the electron
travels to will be determined by the amount of energy in the photon.
• The electron cannot maintain this higher energy level and eventually returns to a lower level.
• The energy is released as it travels down in the form of EMR.
• The color you see depends on the wavelength of the light released.
Determining the Energy of the photon.
• To determine the Energy of the photon released, we use the formula
E=h ν
Example:
• PROBLEM:What is the energy of a photon with a frequency of 3.7 x 107Hz?
• SOLUTION:Use the formula E=h ν.E = ? h= 6.6261 x 10-34 J-s ν = 3.7 x 107Hz
E= (6.6261 x 10-34 J-s ) (3.7 x 1071/s)= 24.51657 x 1027 JThen 24.51657 is not a number between 1 and 10.2.451657 x 10 28 J