1. Light!

2. Where does light come from?
Light is the result of electromagnetic radiation from an energized (usually heated) body of matter.
Most often thought of as “visible light”, but electromagnetic radiation occurs over a large spectrum of wavelengths.

3. Electromagnetic radiation occurs at different wavelengths, from long radio waves, to short gamma rays.

4. Energy and Wavelength
The energy of the light wave (radiation) is directly related to its frequency and wavelength.

5. High Energy Light Waves
Increasing frequency (decreasing wavelength) increases energy

6. Chemistry and Light
We have already seen that light emission results from electrons during the excitation from and emission of radiation.

7. Emission
Emission of radiation (light energy) occurs when an electron drops from an excited state
Electron absorbs energy from an outside source (flame, solar radiation)
Added energy causes it to jump to a higher energy level
Electron is very unstable at the higher energy level and quickly drops back down to its “ground state”, releasing energy as it drops.

8. Bohr’s Back!
Each energy level has a “quantized” amount of energy that each electron occupying it holds.
So, electrons dropping between the same levels ALWAYS release the same amount of energy

9. Energy and Wavelengths
The energy of emitted radiation (light) is directly related to the wavelength of the light Emission Animation
Dropping to n=1 : UV Light
Dropping to n=2 : Visible Light
Dropping to n=3 : IR Light

10. Emission and Chemistry
Emission is used all the time to determine the elemental composition of samples because each element has a unique set of wavelengths it emits.
The trick is being able to see all of the wavelengths present in a sample of light

11. Flame Test Gave signature “colors” of emission for different elements
Limits
Only useful for metals
Need a lot of sample to heat to see the color
Only see color that results from mixture of all the wavelengths present. (What if 2 are orange?!?)

12. Spectroscopy – Fancy Flame Test
Spectroscopy uses a prism or grating to separate out all of the individual wavelengths present in a light source

13. Spectroscopy
The separated wavelengths proved a unique “signature” for each element.

14. Applications of Spectroscopy
Determining the elements present in unknown samples
Mars Rover (soil/rock samples)

15. Applications of Spectroscopy
Determining the elements present in celestial bodies
Stars, Gas Clouds

16. Applications of Spectroscopy
Determining the concentration of solutions
Measures how much light is absorbed by the sample, showing the amount of dissolved molecules present