Chemical Education Today
Report: My Favorite Element
My Favorite Element: Silicon by Thomas H. Lane
Just the Facts, Please!
Did You Know?
The atomic symbol for silicon is Si and its atomic mass is 28.0855. Silicon is found in Group IV of the periodic table of elements, as is carbon. Historically, this close family relationship to carbon has led many scientists to undertake the investigation of organosilicon chemistry in the belief that a new realm of chemistry awaited discovery. They were absolutely correct in their belief ! Just as Mark Twain was beginning his literary career (1863), Friedel and Crafts published the first synthesis of a silicon–carbon bond that opened a completely new branch of chemistry: organosilicon chemistry.
Silicon is believed to play an active role in the development of plants and animals. Unfortunately, the mechanisms and processes remain a complete mystery. Scientists have observed that the silicon content of living organisms appears to decrease as the complexity of the organism increases; why? In the human body there is usually only 5 to 10 grams of silicon, which is most likely acquired from the environment. Silicon plays a key, but not fully understood, role in the growth of hair, nails, bones, and feathers. At the site of a bone fracture, silicon content increases 50-fold in the collagen web. There is so much more to learn and do with silicon—but nature gives up her secrets sparingly! Silicon has been very good to me. It has allowed me to make a difference—to enhance the well being of the people of this planet. I have helped to make the stuff (mostly organosilicon stuff ) that you use every day. I named my son, Samuel Isaac Lane—SILANE, the simplest of the silicon compounds (SiH4)—a volatile pyrophoric compound with incredible potential. Although I doubt that he will study his name sake, I challenge you—the next generation of explorers and chemists— to pick up where others have left off. Remember, as chemists we improve people’s lives through the transforming power of chemistry—make some of that chemistry silicon chemistry.
Second only to oxygen in its natural abundance in the Earth’s crust (by mass, 25.7%), silicon is found in nearly 98% of all mineral forms. It has many compounds and substances that have contributed so much to humanity. Silicon itself is not found in nature as the element, but as its oxide, silica (sand, rock, crystal, flint, jasper, amethyst, and so on). Commercially, it is the sole source of elemental silicon, and silica is used in large quantities as a constituent of building materials, ceramics, concretes, and glasses. In its various amorphous forms, it is used as a desiccant, adsorbent, reinforcing agent, binder, builder for detergents, and as a catalyst component for support. Today, we could not live without silicon-based materials. From high purity silica for fiber-optic cables and the communication superhighway to a silicon chip for our phones, computers, game systems, and control circuits for nearly anything that requires a battery or a plug. Silicon-based materials positively impact our lives every day and are among the most studied materials in history! It Has Been around Since the Beginning Silicon is a ubiquitous element that has been helping people on this planet since the first appearance of man. Homo erectus (500,000 BCE) and Neanderthals (70,000 BCE) used simple tools made of granite, quartz, flint, and obsidian (all silicon based). Even the word silicon (silicium) comes from the Latin for flint, silex. These flint artifacts and the earliest silicate pottery provide us with an anthropological framework from which we can gauge the technological achievements and advancements of early societies. As human needs expanded beyond simple utensils and tools for survival, glass and ceramic technologies grew in response.
Little of the chemistry of silicon can be directly inferred from its nearest neighbor, carbon, without a few surprises. Silicon is not carbon and its chemistry proves it! Silicon can expand its coordination number from four to five and even six! Anything you can put on silicon, you can shuffle off with catalytic redistribution. Silicon chemistry represents some of the best (and worst) tradition of organic and inorganic chemistry. 1132
Thomas H. Lane, President of the American Chemical Society in 2009, is scientist emeritus at Dow Corning Corp., Midland, MI 48686;
[email protected].
Silicon ingot.
Breaking a silicon wafer.
Solid State Resources CD-ROM
Not Just a Chubby Carbon
Supporting JCE Online Material
http://www.jce.divched.org/Journal/Issues/2009/Oct/abs1132.html Abstract and keywords Full text (PDF) Supplements: 2 QuickTime movies showing breaking (shattering) of a silicon wafer. From Lisensky, G. C.; Blackwell, J. M.; Ellis, A. B. Solid State Resources CD-ROM, J. Chem. Educ. Software, 1998, SP-12.
Chemistry Comes Alive! Vol. 4
Don’t Tread on Me!
Journal of Chemical Education • Vol. 86 No. 10 October 2009 • www.JCE.DivCHED.org • © Division of Chemical Education
