Spectral Analysis GT Chem 10/27/14

Drill How do you calculate valence? How many valence electrons do these elements have? O Xe Fe Ba HW: pg. 9 Valence electrons

Objectives IWBAT Calculate valence for any element. Use a spectroscope to view spectra from various light sources. Observe continuous and bright-line spectra. Draw the spectrum of light given off from an incandescent lamp, fluorescent lamp and H, He, Ar and Ne vapor lamps. Compare and contrast continuous and emission spectra.

Let’s finish the notes on spectra from yesterday

Emitted Light Color is seen if the electron falls back to energy level n = 2 This is visible light The amount an e- falls determines the frequency of EM radiation released (n = 1 = UV; n = 3 infrared)

Emitted Light No two elements give off the same spectra of colors, because they vary in the number of protons and electrons Emit their own unique line spectra Can be used to identify elements

Line Spectra Emission Spectra of Hydrogen 1 nm = 1 x 10-9 m = “a billionth of a meter”

Emission Spec Lab You will each be working independently to observe the emission spectra. You will need: Colored pencils A spectroscope First, we will observe: Incandescent light Fluorescent light

Incandescent vs. Fluorescent How are they different? Write a description under each to explain the differences.

Types of Spectra The incandescent lamp spectrum should have been a continuous blend of color. We call this a continuous spectrum. The fluorescent lamp spectrum should have been a black background with bright colored lines. This is called an emission (or bright line spectrum)

Examples Scientists in the nineteenth century quickly figured out that each element generates its own unique set of wavelengths of emission or absorption. Below are the emission spectra of helium and carbon.

Continuous Spectrum Solids, liquids, and dense gases emit light of all wavelengths, without any gaps. We call this a continuous spectrum. http://spiff.rit.edu/classes/phys314/lectures/spectra/spectra.html

In the lab… Use a spectroscope to look at each lamp. Use colored pencils to draw what you see. Please do not touch the vapor lamps: you can damage the lamps with the oil on your hands and there is a chance of electrocution. Bend down to the level of the vapor lamp to see a correct spectrum.

When done… Star Spectra WS Let’s use the spectra on this worksheet to identify the composition of various stars. Did you read over this last night? Does it make more sense now?

Wrap-Up Did you know that each element on the Periodic Table has it’s own spectrum? How do you think this information could be used? How could you observe a spectrum of something that is NOT a gas?