Atomic Spectra. Continuous Spectra The (Visible) Hydrogen Spectrum.
Unit 4 Atomic Physics and Spectra. The Electromagnetic Spectrum.
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Transcript of Unit 4 Atomic Physics and Spectra. The Electromagnetic Spectrum.
![Page 1: Unit 4 Atomic Physics and Spectra. The Electromagnetic Spectrum.](https://reader036.fdocuments.in/reader036/viewer/2022081504/56649d045503460f949d7885/html5/thumbnails/1.jpg)
Unit 4
Atomic Physics and Spectra
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The Electromagnetic Spectrum
![Page 3: Unit 4 Atomic Physics and Spectra. The Electromagnetic Spectrum.](https://reader036.fdocuments.in/reader036/viewer/2022081504/56649d045503460f949d7885/html5/thumbnails/3.jpg)
Waves
• type of disturbance that can propagate or travel.
wavelle lnlgth ()
crest
amplitude (A)
velocity (v)trough
Wavelength () is a distance, so its units are m, cm, or mm, etc.
Period (T): time between crest (or trough) passages
Frequency (n): rate of passage of crests (or troughs
c= n
(units: Hertz or cycles/sec)
Equilibrium position
![Page 4: Unit 4 Atomic Physics and Spectra. The Electromagnetic Spectrum.](https://reader036.fdocuments.in/reader036/viewer/2022081504/56649d045503460f949d7885/html5/thumbnails/4.jpg)
• Shorter wavelength (l) = higher frequency (n) and therefore higher energy
![Page 5: Unit 4 Atomic Physics and Spectra. The Electromagnetic Spectrum.](https://reader036.fdocuments.in/reader036/viewer/2022081504/56649d045503460f949d7885/html5/thumbnails/5.jpg)
Waves bend when they pass through material of different densities.
swimming pool
air
water
prismairair
glass
Refraction
![Page 6: Unit 4 Atomic Physics and Spectra. The Electromagnetic Spectrum.](https://reader036.fdocuments.in/reader036/viewer/2022081504/56649d045503460f949d7885/html5/thumbnails/6.jpg)
All radiation (including visible light) travels as Electromagnetic waves.
Examples of objects with magnetic fields:Magnetthe Earththe Sun
Examples of objects with electric fields:Electrical appliancesLightningProtons, electrons
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Electromagnetic Radiation
How we get information about the cosmos
e.g. Visible Light
![Page 8: Unit 4 Atomic Physics and Spectra. The Electromagnetic Spectrum.](https://reader036.fdocuments.in/reader036/viewer/2022081504/56649d045503460f949d7885/html5/thumbnails/8.jpg)
nc =
1 nm = 10 -9 m , 1 Angstrom = 10 -10 m
The Electromagnetic Spectrum
![Page 9: Unit 4 Atomic Physics and Spectra. The Electromagnetic Spectrum.](https://reader036.fdocuments.in/reader036/viewer/2022081504/56649d045503460f949d7885/html5/thumbnails/9.jpg)
When you bend light, bending angle depends on wavelength, or color.
Refraction of light
(Prism demo)
![Page 10: Unit 4 Atomic Physics and Spectra. The Electromagnetic Spectrum.](https://reader036.fdocuments.in/reader036/viewer/2022081504/56649d045503460f949d7885/html5/thumbnails/10.jpg)
Types of Spectra
1. "Continuous" spectrum luminous solid, liquid, or dense gas, emits
light of all wavelengths, produces a continuous spectrum
2. "Emission" spectrum low-density, hot gas emits light whose
spectrum consists of a series of bright emission lines that are characteristic of the composition of the gas.
1. "Absorption” Spectrum cool, thin gas absorbs certain wavelengths
from a continuous spectrum, leaving dark absorption lines in their place, superimposed on the continuous spectrum.
![Page 11: Unit 4 Atomic Physics and Spectra. The Electromagnetic Spectrum.](https://reader036.fdocuments.in/reader036/viewer/2022081504/56649d045503460f949d7885/html5/thumbnails/11.jpg)
Pattern of lines is a fingerprint of the element
![Page 12: Unit 4 Atomic Physics and Spectra. The Electromagnetic Spectrum.](https://reader036.fdocuments.in/reader036/viewer/2022081504/56649d045503460f949d7885/html5/thumbnails/12.jpg)
For a given element, emission and absorption lines occur at the same wavelengths.
Sodium emission and absorption spectra
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The Particle Nature of Light
Light interacts with matter as individual packets of energy, called photons.
photon energy is proportional to frequency:
example: ultraviolet photons are more dangerous than visible photons.
![Page 14: Unit 4 Atomic Physics and Spectra. The Electromagnetic Spectrum.](https://reader036.fdocuments.in/reader036/viewer/2022081504/56649d045503460f949d7885/html5/thumbnails/14.jpg)
The Nature of Atoms
The Bohr model of the Hydrogen atom:
_
+
proton
electron
"ground state"
_
+
"excited state"
![Page 15: Unit 4 Atomic Physics and Spectra. The Electromagnetic Spectrum.](https://reader036.fdocuments.in/reader036/viewer/2022081504/56649d045503460f949d7885/html5/thumbnails/15.jpg)
When an atom absorbs a photon, it moves to a higher energy state briefly
When it jumps back to lower energy state, it emits photon(s) in a random direction, conserving the total energy of the system
![Page 16: Unit 4 Atomic Physics and Spectra. The Electromagnetic Spectrum.](https://reader036.fdocuments.in/reader036/viewer/2022081504/56649d045503460f949d7885/html5/thumbnails/16.jpg)
Other elements
Helium Carbon
neutron proton
Each element has its own allowed energy levels yielding a unique spectral fingerprint.
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Atmospheric blocking
![Page 18: Unit 4 Atomic Physics and Spectra. The Electromagnetic Spectrum.](https://reader036.fdocuments.in/reader036/viewer/2022081504/56649d045503460f949d7885/html5/thumbnails/18.jpg)
Radio Waves
• Emitted by TV, radio, stars, galaxies
• Radio wave image of CO gases in our Milky Way galaxy
![Page 19: Unit 4 Atomic Physics and Spectra. The Electromagnetic Spectrum.](https://reader036.fdocuments.in/reader036/viewer/2022081504/56649d045503460f949d7885/html5/thumbnails/19.jpg)
Microwaves
• Penetrate clouds, fog communication, radar
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Infrared• Thermal (heat)
IR image of Milky Way
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Visible
• Detection with eyes
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Ultraviolet
• Higher energy than visible light
UV image of the Sun
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X ray radiation
X ray image of the Sun
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Gamma-rays
• Shortest wavelength, therefore highest E• Produced by supernovae, pulsars, black holes, …• Gamma ray bursts (source ???)
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• http://science.hq.nasa.gov/kids/imagers/ems/gamma.html
• https://www.e-education.psu.edu/astro801/content/l3_p4.html