Key Questions

Counterintuitive Examples

Analogies and Metaphors

Pictures in the Mind

Language of Chemistry

lithosphere the upper portion of the earth’s crust.

mineral inorganic solid of definite composition found in the earth’s crust.

silicates minerals with crystal structure containing silicon-oxygen tetrahedra.

supercooling process of cooling a liquid below its freezing point without changing to a solid.

Silica and silicates are compounds made primarily of silicon and oxygen atoms.

They can be discussed to make three important points:

1. Many minerals are silicate based.
2. Lewis structure pictures can be used to classify minerals.
3. Lewis structure pictures can help explain physical properties of minerals.

All silicate minerals contain Si atoms bonded to four O atoms in a tetrahedral arrangement. The simplest involve the orthosilicate ion (SiO 4 4– ).

Each oxygen is bonded to only one Si and has a residual negative charge. Examples of orthosilicate minerals are zircon (ZrSiO 4 ) and forsterite (Mg 2 SiO 4 ).  

When an oxygen atom is shared by two Si atoms, the pyrosilicate anion (Si 2 O 7 6– ) is obtained. 

The Lewis structure shows single bonds, octets on each atom, and a tetrahedral geometry around the Si atom. Some pyrosilicate minerals are akermanite (Ca 2 MgSi 2 O 7 ), lawsonite (CaAl 2 Si 2 O 7 (OH)2 ), and hemimorphite (Zn 4 (OH)2 Si 2 O 7 ). 

The silicate units can continue to link through sharing oxygen atoms to form long single chains of the general formula SiO 3 2–

A logical extension of this build-up of tetrahedra is to have all four oxygens in a tetrahedral silicate unit shared by Si atoms in adjacent units. The result is quartz, with an empirical formula of SiO 2 . The quartz structure can be imagined by viewing the three-dimensional linked structure of diamond.  SiO 2 would have Si’s where each C is in the diamond structure; the oxygen atoms are then midway between each pair of Si atoms. 

The one-, two-, or three-dimensional links of SiO x units lead to their physical properties. Asbestos is mixed minerals of the long, double-chain type. Thus, they are needle-like, which may account for some of the damage they do to living tissue. Micas are slippery due to two-dimensional sheets of SiO x units that can slide over each other. Quartz has structural strength because of its three-dimensional covalent linking of SiO x units.

The part of the molar mass due to oxygen can be calculated as a percentage of the whole:

Sample Problems: Calculate the percent oxygen in the minerals:

1. Calcite, CaCO 3 [48.0%]
2. Corundum, Al 2 O 3 [47.1%]
3. Gypsum, CaSO 4 ·2H 2 O [59.2%]
4. Hematite, Fe 2 O 3 [30.1%]
5. Orthoclase (K-feldspar), K(AlSi 3 O 8 ) [50.1%]

Words about concepts in this module can be obtained from the clues given.

Find these words in the block of letters:

1. Silicates are compounds made primarily of oxygen and this element.
2. A gem whose basic mineral is Al 2 O 3 with Cr(III) as an impurity.
3. This property of gemstones is characterized by presence of transition elements as impurities.
4. This gemstone is an allotrope of carbon.
5. Most abundant element in the earth’s crust, by mass.
6. Inorganic solid of definite composition found in the crust.
7. Silicates have this geometrical arrangement.
8. Rock candy is this organic compound.
9. One of the six basic crystal systems.
10. A lavender flame test identifies this element.

Answers:

1. SILICON
2. RUBY
3. COLOR
4. DIAMOND
5. OXYGEN
6. MINERAL
7. TETRAHEDRAL
8. SUCROSE
9. MONOCLINIC
10. POTASSIUM

1. "The Chemistry of Earth": reinforcing chemistry topics through examples from geology—solubility, precipitation, equilibrium, and acid-base chemistry applied in explaining mineral deposition and  world-wide distribution of ores and silicate minerals; the relationship between chemical structure and macroscopic properties—cave formation and stalactite and stalagmite development; limestone.
2. "The Atmosphere": Common theory on formation of the atmosphere; the composition today—highlights of some environmental concerns: contaminants being added to the atmosphere, the greenhouse effect, the hole in the ozone layer, the commercial use of CFC’s.
3. "Chemical Bonds": Ionic and covalent bonds defined through graphic illustration — a comparison of their relative strength in ionic crystals (sodium chloride) and network covalent solids (diamond)—molecular solids; the difference between the strong intramolecular covalent bonds between atoms in a molecule and the weaker intermolecular attractions, such as hydrogen bonds, between molecules.

3. MECC (Minnesota Educational Computer Consortium, St. Paul, MN 55165): "Murphy’s Minerals," a computer game to practice skills learned in identifying minerals. (612) 569-1500.Planet Earth Series: A seven-part video series that was first shown on the Public Broadcasting Service in 1986. This series is a rich and exciting investigation of the earth sciences today, a vivid panorama of the planet we call home. Produced by WQED/Pittsburgh, in association with the National Academy of Sciences, this series includes the episodes: "The Living Machine," "The Blue Planet," "The Climate Puzzle," "Tales from Other Worlds," "Gifts from the Earth," "The Solar Sea," and "Fate of the Earth."

           The episode most useful with this topic is "Gifts from the Earth." This program acquaints students with the breadth and variety of the world’s natural resources             through a story spanning millions of years. Included are segments explaining how mineral-saturated hydrothermal vents on the sea floor ultimately became gold             and copper mines on land; about the slow accumulation of fossil fuels; of the ingenious scientists who seek out the secrets of the earth. The formation of metallic             elements, minerals—both precious and common—are explored, as well as how these resources influence civilization. One of the handouts, "Minerals in Our              Lives," is particularly interesting as it lists 60 common  elements and compounds readily available from the earth’s crust and describes uses of each. Available              from: PBS Video, 1320 Braddock Place, Alexandria, VA 22314. Telephone: (703) 739-5000.

            The episode "The Blue Planet" deals primarily with the influence of liquid water on the surface of the earth, and could also be used in this module.

4. "Gemstones of America," STS Film & Video Productions, P.O. Box 27477, Salt Lake City, UT 84127. A Smithsonian Project, 1991. (801) 263-3959.
5. Software published by JCE: Software, a publication of the Journal of Chemical Education, Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706-1396: (608) 262-5153 (voice) or (608) 262-0381 (FAX).

1. KC? Discoverer with Knowledgeable Counselor, by Daniel Cabrol, John W. Moore and Robert C. Rittenhouse. Special Issue 2, for IBM PS/2, PC compatible computers.
2. KC? Discoverer: Exploring the Properties of the Chemical Elements, by Aw Feng and John W. Moore. Vol. I B, No. 1, for IBM PS/2, PC compatible computers.
3. KC? Discoverer?, by Michael Liebl, Vol. IV A, No. 2, for all Apple II computers.
4. The Periodic Table Stack, by Michael Farris. Vol. I C, No. 1, for the Apple Macintosh.

6. Software published by Project SERAPHIM, Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706-1396: (608) 263-2837 (voice) or (608) 262-0381 (FAX).

1. For the Apple II computer: AP 807
2. For IBM PS/2 PC-compatible computers: PC 3702

7. Videodiscs published byJCE: Software, a publication of the Journal of Chemical Education, Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706-1396: (608) 262-5153 (voice) or (608) 262-0381 (FAX).

1. "Earth’s Atmosphere," "Acid Rain and Limestone" and "Silicates," three chapters on The World of Chemistry: Selected Demonstrations and Animations: Disc II (double sided, 60 min.), Special Issue 4.
2. The Periodic Table Videodisc (single side, 30 min.). Special Issue 1.