Light Emission Spectra & The Quantum Mechanical Model

1. Light Emission Spectra & The Quantum Mechanical Model

3. “The Sun” It is important to keep in mind that we can only ‘see’ a small fraction of the universe’s energy

5. The Visible light Spectrum • Light is characterized by frequency, or more commonly, by wavelength • Visible light spans from 400 nm to 700 nm • or 0.4 m to 0.7 m; 0.0004 mm to 0.0007 mm, etc.

6. The Visible light Spectrum

7. White light • White light is the combination of all wavelengths, with equal representation • “red hot” poker has much more red than blue light • experiment:red,green, andbluelight bulbs makewhite • RGB monitor combines these colors to displaywhite combined, white light called additive color combination—works with light sources wavelength blue light green light red light

8. Additive Colors • Red, Green, andBluelight sources can be used to synthesize almost any perceivable color • Red+Green= Yellow • Red+ Blue= Magenta • Green + Blue = Cyan • These three dual-source colors become the primary colors for subtraction • why? because absence of green is magenta • absence ofredis cyan, etc.

9. Light Spectra White light contain all colors of light Hot Matter in condensed states (solid or liquid or dense gas) nearly always emits radiation with a continuous spectrum. called Incandescence When the atoms are in a condensed state, the electrons can make transitions not only within the energy levels of their own atom, but also between the levels of neighboring atoms.

10. Atomic Emission Line Spectra Each element has different wavelengths of light given off when its electrons are excited - an atomic finger print

11. Atomic Absorption Spectra The white light passing through a cool gas can absorb wavelengths of light to create an absence of color.

12. Emission vs. Absorption

13. QMM and electron excitation The color of light given off depends on the amount of energy absorbed The larger the atom the more energy can be absorbed, and more excitation lines produced

14. Excitation E2 Energy E1 Nucleus 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.

15. Energy E2 E1 Emission A quantum of energy in the form of light (photon) is emitted when the electron drops back to a lower energy level.

16. Example Atomic Emissions Sodium Helium Krypton

17. Example Atomic Emissions Remember that each element has discrete emission lines that can be measured to define their “atomic fingerprint”

18. Mercury Emission Mercury Metal Mercury Vapor Lamp

19. Multiple Source Emissions Pure Mercury