1. Emission Spectrum of Hydrogen
1 nm = 1 x 10-9 m = “a billionth of a meter”
410 nm
434 nm
486 nm
656 nm

2. Emission Spectrum of an Element
1 nm = 1 x 10-9 m = “a billionth of a meter”
410 nm
434 nm
486 nm
656 nm
1 nm = 1 x 10-9 m = “a billionth of a meter”

3. Continuous and Line Spectra
Visible
spectrum
l (nm)
light nm Na H
Spectroscopy is a method of identifying unknown substances from their spectra. Because all materials have unique spectra, you can think of these spectra as being molecular fingerprints.
Line spectra of selected elements showing the emission spectra or fingerprint of that element.
The unique set of lines produced is due to the fact that electrons are falling from different excited states in the atoms to the ground state.
Objects at high temperature emit a continuous spectrum of electromagnetic radiation.
A different kind of spectrum is observed when pure samples of individual elements are heated.
When the emitted light is passed through a prism, only a few narrow lines, called a line spectrum, are seen rather than a continuous range of colors.
Using Planck’s equation, the observation of only a few values of  (or ) in the line spectrum meant that only a few values of E were possible — only states that had certain values of energy were possible or allowed.
Any given element has both a characteristic emission spectrum and a characteristic absorption spectrum, which are complementary images.
– Emission spectrum: emission of light by atoms in excited states
– Absorption spectrum: absorption of light by ground-state atoms to produce an excited state
• Emission and absorption spectra form the basis of spectroscopy, which uses spectra to provide information about the structure and composition of a substance or an object Ca Hg
4000 A o
5000
6000
7000

4. Continuous and Line Spectra
5000
6000
7000
light Na H
Line spectra of selected elements showing the emission spectra or fingerprint of that element.
The unique set of lines produced is due to the fact that electrons are falling from different excited states in the atoms to the ground state. Ca Hg
4000 A o
5000
6000
7000

5. Flame Emission Spectra
Photographs of flame tests of burning wooden splints soaked in different salts.
This technique is called emission spectroscopy.
methane gas
wooden splint
sodium ion
calcium ion
copper ion
strontium ion
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6. Copyright © 2006 Pearson Benjamin Cummings. All rights reserved.

7. Flame Tests for Certain Metals
BORAX BEAD TESTS FOR CERTAIN METALS
(All beads formed in the oxidizing flame)

8. Fireworks

9. Fireworks The chemistry of fireworks
– Colors of fireworks due to atomic emission spectra
– A typical shell used in a fireworks display contains gunpowder to propel the shell into the air and a fuse to initiate a variety of redox reactions that produce heat and small explosions
– Thermal energy excites the atoms to higher energy states, and as they decay to lower energy states, the atoms emit light that gives the familiar colors
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

10. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

11. Common chemicals used in the manufacture of fireworks
Oxidizers Fuels (Reductants) Special Effects
Ammonium perchlorate aluminum Blue flame: copper carbonate, copper sulfate, or copper oxide
Barium chlorate antimony sulfide Red flame: strontium nitrate or strontium carbonate
Barium nitrate charcoal White flame: magnesium or aluminum
Potassium chlorate magnesium Yellow flame: sodium oxalate or cryolite (Na3AlF6)
Potassium nitrate sulfur Green flame: barium nitrate or barium chlorate
Potassium perchlorate titanium White smoke: potassium nitrate plus sulfur
Strontium nitrate Colored smoke: potassium chlorate and sulfur, plus organic dye
Whistling noise: potassium benzoate or sodium salicylate
White sparks: aluminum, magnesium, or titanium
Gold sparks: iron filings or charcoal
Almost any combination of an oxidizer and a fuel may be used along with the compounds needed to produce a desired special effect.
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

12. Composition of Fireworks
Gunpowder
Sulfur, charcoal, potassium nitrate (saltpeter)
Salts (to give color)
Red = lithium
Green = copper

13. Electron Energy Levels
nucelus
1st energy level
2nd energy level
3rd energy level
1999, Addison, Wesley, Longman, Inc.
Energy
absorbed
Energy
lost