Chapter 5 Electrons in Atoms. Wave Nature of Light Electromagnetic radiation which is a form of...
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Transcript of Chapter 5 Electrons in Atoms. Wave Nature of Light Electromagnetic radiation which is a form of...
![Page 1: Chapter 5 Electrons in Atoms. Wave Nature of Light Electromagnetic radiation which is a form of energy that exhibits wavelike behavior as it travels through.](https://reader035.fdocuments.net/reader035/viewer/2022062322/56649eff5503460f94c154e8/html5/thumbnails/1.jpg)
Chapter 5
Electrons in Atoms
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Wave Nature of Light
• Electromagnetic radiation which is a form of energy that exhibits wavelike behavior as it travels through space.
• Examples: light, radio waves, x-rays, etc
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Parts of a Wave
wavelength
amplitude
amplitude
crest
trough
wavelength
origin
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Wavelength
• Waves have a repetitive nature.• Wavelength- ( lambda)
– shortest distance between corresponding points on adjacent waves.
– Measured in units like meters, centimeters, or nanometers depending on the size.
– 1 x 10-9 meters = 1 nanometer
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Frequency• # of waves that pass a given point per
second.• Units are waves/sec, cycles/sec or
Hertz (Hz)• Abbreviated the Greek letter nu or
by an f
c = f
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Frequency and wavelength
• Are inversely related
• As one goes up the other goes down.
High frequency, Short Wavelength
Low frequency, Long Wavelength
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Wave Formula
• All electromagnetic waves, including visible light, travel at the speed of 3.00 x 10 8 m/s in a vacuum.
• Speed of light = c = 3.00 x 108 m/s
c=fSpeed of light = (wavelength) x (frequency)
![Page 8: Chapter 5 Electrons in Atoms. Wave Nature of Light Electromagnetic radiation which is a form of energy that exhibits wavelike behavior as it travels through.](https://reader035.fdocuments.net/reader035/viewer/2022062322/56649eff5503460f94c154e8/html5/thumbnails/8.jpg)
Example Problem
• What is the wavelength of a microwave having a frequency of 3.44 x 109 Hz?
Formula: c=f = ?f = 3.44 x 109 Hzc = 3.00 x 108 m/s
3.00 x 108 m/s = (3.44 x 109 s-1)3.00E8 / 3.44E9 = 8.72 x 10-2 m
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Practice
• What is the frequency of green light, which has a wavelength of 5.90 x 10-7m?
• A popular radio station broadcast with a frequency of 94.7MHz, what is the wavelength of the broadcast? ( frequency needs to be is Hz)
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• Different frequencies produce different types of waves.
• The entire range of frequencies is called the electromagnetic spectrum
• We are only able to see with our eyes a small portion of the spectrum = visible light
• ROY G BIV• Different colors mean different
frequencies/wavelengths
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Energy & The Spectrum
• The energy of a wave increases with increasing frequency
• High Frequency = High Energy• Low Frequency = Low Energy• Blue light has more energy than Red light
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Low energy
High energy
Low Frequency
High Frequency
Long Wavelength
Short Wavelength
Radiowaves
Microwaves
Infrared .
Ultra-violet
X-Rays
GammaRays
Visible Light
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Quanta
• Max Planck suggested the idea of quanta or packets of energy.
• Quanta is the minimum amount of energy that can be lost or gained by an atom.
• Energy is quantized = it comes in packets (like stairs or pennies only whole numbers)
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Planck’s Constant
• h = 6.626 x 10-34 J.s (Joule seconds)Energy = (Planck’s constant)(frequency)
E = h fExample: What is the energy in Joules of a photon from the violet
portion of the rainbow if it has a frequency of 7.23 x 1014 Hz?E = ?h = 6.626 x 10-34 Jsf = 7.23 x 1014 Hz (or s-1)
E = (6.626 x 10-34 Js)(7.23 x 1014 s-1) E = 4.79 x 10-19 J
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Photoelectric Effect• In the 1900s, scientist studied interactions of
light and matter.• One experiment involved the photoelectric
effect, which refers to the emission of electrons from a metal when light shines on the metal.
• This involved the frequency of the light. It was found that light was a form of energy that could knock an electron loose from a metal.
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Photon
• Light waves can also be thought of as streams of particle.
• Einstein called these particles photons (He won a Nobel Prize for this)
• A photon is a particle of electromagnetic radiation having zero mass and carrying a quantum energy.
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Bohr’s Model
• Why don’t electrons fall into nucleus?
• Bohr suggested that they move like planets around sun.
• Certain amounts of energy separate one level from another.
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• Nucleus is found inside a blurry “electron cloud”
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Bohr’s Model
Nucleus
Electron
Orbit
Energy Levels
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Bohr’s Model• Further away
from nucleus means more energy.
• There is no “in between” energy
• Energy LevelsIncr
easi
ng e
nerg
y
Nucleus
First
Second
Third
Fourth
Fifth
}
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Bohr Model of the Atom• Ground state- the lowest energy state of an
atom.• Excited state – state in which an atom has a
higher potential energy than its ground state.• Energy is quantized. It comes in chunks.• quanta - amount of energy needed to move from
one energy level to another.• Since energy of an atom is never “in between”
there must be a quantum leap in energy.
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Bohr Energy Levels
• K = 2 electrons – 1st• L = 8 electrons – 2nd• M = 18 electrons – 3rd• N = 32 electrons – 4th
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Heisenberg Uncertainty Principle
• This is the theory that states that it is impossible to determine simultaneously both the position and velocity of an electron or any other particle.
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Quantum Theory• Schrodinger derived an equation that
described energy & position of electrons in atom
• Schrodinger along with other scientists laid the foundation for the modern quantum theory, which describes mathematically the wave properties of electrons and other very small particles.