1. Chapter 4

2. 4.1 Spectral Lines NO radiation emits a perfect blackbody spectrum
All spectra deviate from this ideal by a lot or just a very small amount
These deviations tell us the about the physical conditions

3. 4.1 Spectral Lines Spectroscope- a device used to analyze radiation
Consists of an opaque barrier with a slit, a prism, and an eyepiece

4. 4.1 Spectral Lines
Continuous spectra- spectrum in which the radiation is distributed over all frequencies
Example: the black body radiation emitted by a hot dense body

5. Emission Lines- narrow “slices” of the continuous spectrum
4.1 Spectral Lines

6. 4.1 Spectral Lines
Absorption lines- dark lines that interrupt a continuous spectrum- representing wavelengths “absorbed” by gases present in the outer layers of the sun, or Earth’s atmosphere
Now referred to as “Fraunhofer Lines”

7. spectroscopy- the analysis of the ways in which matter emits and absorbs radiation
4.1 Spectral Lines

8. 4.1 Spectral Lines Kirchhoff’s Laws:
A luminous solid or liquid, or a sufficiently dense gas, emit light of all wavelengths and so produces a continuous spectrum of radiation
A low-density hot gas emits light whose spectrum consists of a series of bright emission lines. These lines are characteristic of the chemical composition of the gas
A cool, thin gas absorbs certain wavelengths from a continuous spectrum, leaving dark absorption lines in their place

9. 4.2 The Formation of Spectral Lines
Bohr Model

10. 4.2 The Formation of Spectral Lines
Photons- a particle of electromagnetic radiation

11. 4.3 Molecules
Molecule- tightly bound group of atoms held together by interactions among their orbiting electrons

12. 4.4 Spectral Line Analysis
Spectrographs are attached to telescopes and galactic clouds and stellar dust replace the atmosphere in intervening with the spectral lines

13. 4.4 Spectral Line Analysis
Spectral lines seen from looking at stars are compared to laboratory spectra of known atoms, ions, and molecules to determine the chemical composition of the star