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Physics and the Quantum Mechanical Model
Neon advertising signs are formed from glass tubes bent in various shapes. An electric current passing through the gas in each glass tube makes the gas glow with its own characteristic color. You will learn why each gas glows with a specific color of light.
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Slide 2 of 38
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Physics and the Quantum Mechanical Model
> Light
The wavelength and frequency of light are inversely proportional to each other.
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The product of the frequency and wavelength always equals a constant (c), the speed of light.
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Slide 3 of 38
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Physics and the Quantum Mechanical Model
> Light
• The amplitude of a wave is the wave’s height from zero to the crest.
• The wavelength, represented by (the Greek letter lambda), is the distance between the crests.
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• The frequency, represented by (the Greek letter nu), is the number of wave cycles to pass a given point per unit of time.
• The SI unit of cycles per second is called a hertz (Hz).
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Slide 4 of 38
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Physics and the Quantum Mechanical Model
> Light
According to the wave model, light consists of electromagnetic waves.
• Electromagnetic radiation includes radio waves, microwaves, infrared waves, visible light, ultraviolet waves, X-rays, and gamma rays.
• All electromagnetic waves travel in a vacuum at a speed of 2.998 108 m/s.
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Slide 5 of 38
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Physics and the Quantum Mechanical Model
> Light
Sunlight consists of light with a continuous range of wavelengths and frequencies.
• When sunlight passes through a prism, the different frequencies separate into a spectrum of colors.
• In the visible spectrum, red light has the longest wavelength and the lowest frequency.
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Slide 6 of 38
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Physics and the Quantum Mechanical Model
> Light
The electromagnetic spectrum consists of radiation over a broad band of wavelengths.
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Physics and the Quantum Mechanical Model
>
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Atomic Spectra
Atomic Spectra
What causes atomic emission spectra?
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When atoms absorb energy, electrons move into higher energy levels. These electrons then lose energy by emitting light when they return to lower energy levels.
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Slide 8 of 38
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Physics and the Quantum Mechanical Model
> Atomic Spectra
A prism separates light into the colors it contains. When white light passes through a prism, it produces a rainbow of colors.
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Slide 9 of 38
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Physics and the Quantum Mechanical Model
> Atomic Spectra
When light from a helium lamp passes through a prism, discrete lines are produced.
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Slide 10 of 38
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Physics and the Quantum Mechanical Model
> Atomic Spectra
The frequencies of light emitted by an element separate into discrete lines to give the atomic emission spectrum of the element.
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Mercury Nitrogen
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Physics and the Quantum Mechanical Model
>
Slide 11 of 38
An Explanation of Atomic Spectra
An Explanation of Atomic Spectra
How are the frequencies of light an atom emits related to changes of electron energies?
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Physics and the Quantum Mechanical Model
> An Explanation of Atomic Spectra
In the Bohr model, the lone electron in the hydrogen atom can have only certain specific energies.
• When the electron has its lowest possible energy, the atom is in its ground state.
• Excitation of the electron by absorbing energy raises the atom from the ground state to an excited state.
• A quantum of energy in the form of light is emitted when the electron drops back to a lower energy level.
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Slide 13 of 38
Physics and the Quantum Mechanical Model
> An Explanation of Atomic Spectra
The light emitted by an electron moving from a higher to a lower energy level has a frequency directly proportional to the energy change of the electron.
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Slide 14 of 38
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Physics and the Quantum Mechanical Model
> An Explanation of Atomic Spectra
The three groups of lines in the hydrogen spectrum correspond to the transition of electrons from higher energy levels to lower energy levels.
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Physics and the Quantum Mechanical Model
> An Explanation of Atomic Spectra
Animation 6
Learn about atomic emission spectra and how neon lights work.
