What if there is an element that is similar to the almighty carbon in almost every way, but exhibits none of its functions in nature? That's the mystery of silicon, the most abundant element on Earth, and yet seems to be the unappreciated stepchild of the organic world.
I believe there's more to it that that, no? |
Bruce: [sees the Flash suit] Silica-based quartz sand fabric. Abrasion resistant. Heat resistant.
Barry: Uh... yeah, I do... competitive ice dancing.
Bruce: It's what they use on the space shuttle to prevent it from burning up on re-entry.
Barry: I do... very competitive ice dancing.
Conversation between Bruce Wayne and Barry Allen, Justice League (2017)
Silicon (chemical element symbol Si, atomic number 14) is a member of a group of chemical elements classified as metalloids. It is less reactive than its chemical analog carbon. It is the eighth most common element in the universe (by mass) and is the second most abundant element (after oxygen) in the Earth's crust, making up 25.7 percent of the crust by mass. It occasionally occurs as the pure free element in nature, but is more widely distributed in dusts, planetoids, and planets as various forms of silicon dioxide or silicate.
Various biological systems contain silicon as an essential element. Although only tiny traces of it appear to be required by animals, it is much more important for the metabolism of plants, particularly many grasses. Also, silicic acid (a family of chemical compounds of silicon, hydrogen, and oxygen) forms the basis of the array of protective shells of diatoms.
Silicon has many industrial uses. Elemental silicon is the principal component of most semiconductor devices, particularly integrated circuits or "microchips." Given its importance in semiconductors and high-tech devices, its name has been used for the high-tech region known as Silicon Valley in California. In the form of silica and silicates, silicon forms useful glasses, cements, and ceramics. It is also a component of silicones, a group of various synthetic plastic substances made of silicon, oxygen, carbon, germanium, and hydrogen.
Given that some properties of silicon are similar to those of carbon, some individuals have proposed the possibility of silicon-based living organisms. This possibility, however, seems remote for a variety of reasons, including the absence of a "silicon cycle" (analogous to the carbon cycle), the absence of an appropriate solvent for silicon compounds (analogous to water that dissolves organic compounds), and the inability of silicon to form the diversity of compounds required for living systems.
The name silicon is derived from the Latin word, silex, meaning "flint" or "hard stone," corresponding to the materials now called "silica" or "silicates." It was first identified by Antoine Lavoisier in 1787, as a component of silex, but Humphry Davy (in 1800) mistook it as a compound. In 1811, Joseph Gay-Lussac and Louis Jacques Thénard probably prepared impure amorphous silicon through the heating of potassium with silicon tetrafluoride. The first person to identify it as an element was Jöns Jakob Berzelius, in 1823. In the following year, Berzelius prepared amorphous silicon using approximately the same method as Gay-Lussac. He also purified the product by repeated washing.
Various biological systems contain silicon as an essential element. Although only tiny traces of it appear to be required by animals, it is much more important for the metabolism of plants, particularly many grasses. Also, silicic acid (a family of chemical compounds of silicon, hydrogen, and oxygen) forms the basis of the array of protective shells of diatoms.
Silicon has many industrial uses. Elemental silicon is the principal component of most semiconductor devices, particularly integrated circuits or "microchips." Given its importance in semiconductors and high-tech devices, its name has been used for the high-tech region known as Silicon Valley in California. In the form of silica and silicates, silicon forms useful glasses, cements, and ceramics. It is also a component of silicones, a group of various synthetic plastic substances made of silicon, oxygen, carbon, germanium, and hydrogen.
Given that some properties of silicon are similar to those of carbon, some individuals have proposed the possibility of silicon-based living organisms. This possibility, however, seems remote for a variety of reasons, including the absence of a "silicon cycle" (analogous to the carbon cycle), the absence of an appropriate solvent for silicon compounds (analogous to water that dissolves organic compounds), and the inability of silicon to form the diversity of compounds required for living systems.
The name silicon is derived from the Latin word, silex, meaning "flint" or "hard stone," corresponding to the materials now called "silica" or "silicates." It was first identified by Antoine Lavoisier in 1787, as a component of silex, but Humphry Davy (in 1800) mistook it as a compound. In 1811, Joseph Gay-Lussac and Louis Jacques Thénard probably prepared impure amorphous silicon through the heating of potassium with silicon tetrafluoride. The first person to identify it as an element was Jöns Jakob Berzelius, in 1823. In the following year, Berzelius prepared amorphous silicon using approximately the same method as Gay-Lussac. He also purified the product by repeated washing.
Occurrence
Measured by mass, silicon makes up 25.7 percent of the Earth's crust and is the second most abundant element on Earth, after oxygen. Pure silicon crystals are only occasionally found in nature; they can be found as inclusions with gold and in volcanic exhalations. Silicon is usually found in the form of silicon dioxide (also known as silica), and silicate.
Silica occurs in minerals consisting of (practically) pure silicon dioxide in different crystalline forms. Sand, amethyst, agate, quartz, rock crystal, chalcedony, flint, jasper, and opal are some of the forms in which silicon dioxide appears. They are known as "lithogenic" (as opposed to "biogenic") silicas.
Silicon also occurs as silicates (various minerals containing silicon, oxygen, and one or other metal). These minerals occur in clay, sand, and various types of rock such as granite and sandstone. Asbestos, feldspar, clay, hornblende, and mica are a few of the many silicate minerals.
Silicon is a principal component of aerolites, which are a class of meteoroids, and also is a component of tektites, a natural form of glass.
Notable characteristics
In the periodic table, silicon is located in group 14 (former group 4A), between carbon and germanium. In addition, it lies in period 3, between aluminum and phosphorus. Elemental silicon has a gray color and a metallic luster, which increases with the size of the crystal.
The electronic configuration in the outermost shell of a silicon atom is the same as that of a carbon atom—both types of atoms have four bonding electrons. Consequently, both elements are tetravalent (each atom binding up to four other atoms) and share some chemical properties. Both are semiconductors, readily donating or sharing their four outer electrons, allowing for various forms of chemical bonding.
Silicon is similar to glass in that it is strong but brittle and prone to chipping. Although it is a relatively inert element, silicon reacts with halogens and dilute alkalis. Most acids (except for some hyper-reactive combinations of nitric acid and hydrofluoric acid) do not affect it.
Silicon is widely used in semiconductors because it remains a semiconductor at higher temperatures than the semiconductor germanium, and because its native oxide is easily grown in a furnace and forms a better semiconductor/dielectric interface than almost all other material combinations. The electrical resistance of single-crystal silicon significantly changes under the application of mechanical stress, due to what is called the "piezoresistive effect."
Applications
As the second most common element on earth, silicon is a very useful element that is vital to many human industries and impacts much of modern life. For instance, it is a major component of glass, concrete, and cements of many kinds. In addition, one of its most valuable applications lies in that it forms the fundamental substrate in manufacturing electronics devices such as integrated circuits and power transistors. Further, the element and its compounds find widespread use in explosives and pyrotechnics. Silicon is also used in mechanical seals, caulking compounds, and high-temperature, silicon-based greases.
The largest application of pure (metallurgical grade) silicon is in aluminum-silicon alloys, often called "light alloys," to produce cast parts, mainly for automotive industry. (This represents about 55% of the world consumption of pure silicon.)
The second largest application of pure silicon is as a raw material in the production of silicones (about 40% of the world consumption of silicon)
Pure silicon is also used to produce ultra-pure silicon for electronic and photovoltaic applications:
Ultrapure silicon can be doped with other elements to adjust its electrical response by controlling the number and charge (positive or negative) of current carriers. Such control is necessary for transistors, solar cells, microprocessors, semiconductor detectors and other semiconductor devices which are used in electronics and other high-tech applications. Hydrogenated amorphous silicon is widely used in the production of low-cost, large-area electronics in applications such as LCDs. It has also shown promise for large-area, low-cost thin-film solar cells.
Silicon dioxide or silica in the form of sand and clay is an important ingredient of concrete and brick and is also used to produce Portland cement. Silica from sand is a principal component of glass. Glass can be made into a great variety of shapes and with a many different physical properties. Silica is used as a base material to make window glass, containers, insulators, and many other useful objects. Silicon carbide is one of the most important abrasives. Silicones are flexible compounds containing silicon-oxygen and silicon-carbon bonds; they are widely used in applications such as artificial breast implants and contact lenses. Silicones are also used in many other applications. Silly Putty was originally made by adding boric acid to silicone oil. Now name-brand Silly Putty also contains significant amounts of elemental silicon, silicon binds to the silicone and allows the material to bounce 20 percent higher.
Silicon-based life
Given that silicon is similar to carbon, particularly in its valency, some have pondered over the possibility of silicon-based life. For instance, A. G. Cairns-Smith has proposed that the first living organisms may have been forms of clay minerals, which were probably based around the silicon atom.
Although there are no known forms of life that rely entirely on silicon-based chemistry, there are some that rely on silicon minerals for specific functions. Some bacteria and other forms of life, such as the protozoa radiolaria, have silicon dioxide skeletons, and the sea urchin has spines made of silicon dioxide. These forms of silicon dioxide are known as biogenic silica. Silicate bacteria use silicates in their metabolism.
Yet, life as it is known today could not have developed based on a silicon biochemistry. The main reason is that life on Earth depends on the carbon cycle: Autotrophic organisms use carbon dioxide to synthesize organic compounds with carbon, which is then used as food by heterotrophic organisms, which produce energy and carbon dioxide from these compounds. If carbon were to be replaced by silicon, there would be a need for a silicon cycle, involving the participation of silicon dioxide. However, unlike carbon dioxide, silicon dioxide is a solid that does not dissolve in water and cannot be transported through living systems by common biological means. Consequently, another solvent would be necessary to sustain silicon-based life forms. It would be difficult (if not impossible) to find another common compound with the unusual properties of water that make it an ideal solvent for carbon-based life.
Larger silicon compounds (silanes) that are analogous to common hydrocarbon chains are generally unstable, owing to the larger atomic radius of silicon and the correspondingly weaker silicon-silicon bond. Silanes decompose readily and often violently in the presence of oxygen, making them unsuitable for an oxidizing atmosphere such as our own. Moreover, unlike carbon, silicon does not have the tendency to form double and triple bonds.
Some silicon rings (cyclosilanes) have been synthesized and are analogous to the cycloalkanes formed by carbon, but the cyclosilanes are rare whereas the cycloalkanes are common. Synthesis of the cyclosilanes suffers from the difficulties inherent in producing any silane compound. On the other hand, carbon will readily form five-, six-, and seven-membered rings by a variety of pathways, even in the presence of oxygen.
Silicon's inability to readily form multiple bonds, long silane chains, and rings severely limits the diversity of compounds that can be synthesized from it. Under known conditions, silicon chemistry simply cannot begin to approach the diversity of organic chemistry, a crucial factor in carbon's role in biology.
Some have construed silicon-based life as existing under a computational substrate. This concept, yet to be explored in mainstream technology, receives ample coverage by science fiction authors.
Measured by mass, silicon makes up 25.7 percent of the Earth's crust and is the second most abundant element on Earth, after oxygen. Pure silicon crystals are only occasionally found in nature; they can be found as inclusions with gold and in volcanic exhalations. Silicon is usually found in the form of silicon dioxide (also known as silica), and silicate.
Silica occurs in minerals consisting of (practically) pure silicon dioxide in different crystalline forms. Sand, amethyst, agate, quartz, rock crystal, chalcedony, flint, jasper, and opal are some of the forms in which silicon dioxide appears. They are known as "lithogenic" (as opposed to "biogenic") silicas.
Silicon also occurs as silicates (various minerals containing silicon, oxygen, and one or other metal). These minerals occur in clay, sand, and various types of rock such as granite and sandstone. Asbestos, feldspar, clay, hornblende, and mica are a few of the many silicate minerals.
Silicon is a principal component of aerolites, which are a class of meteoroids, and also is a component of tektites, a natural form of glass.
Notable characteristics
In the periodic table, silicon is located in group 14 (former group 4A), between carbon and germanium. In addition, it lies in period 3, between aluminum and phosphorus. Elemental silicon has a gray color and a metallic luster, which increases with the size of the crystal.
The electronic configuration in the outermost shell of a silicon atom is the same as that of a carbon atom—both types of atoms have four bonding electrons. Consequently, both elements are tetravalent (each atom binding up to four other atoms) and share some chemical properties. Both are semiconductors, readily donating or sharing their four outer electrons, allowing for various forms of chemical bonding.
Silicon is similar to glass in that it is strong but brittle and prone to chipping. Although it is a relatively inert element, silicon reacts with halogens and dilute alkalis. Most acids (except for some hyper-reactive combinations of nitric acid and hydrofluoric acid) do not affect it.
Silicon is widely used in semiconductors because it remains a semiconductor at higher temperatures than the semiconductor germanium, and because its native oxide is easily grown in a furnace and forms a better semiconductor/dielectric interface than almost all other material combinations. The electrical resistance of single-crystal silicon significantly changes under the application of mechanical stress, due to what is called the "piezoresistive effect."
Applications
As the second most common element on earth, silicon is a very useful element that is vital to many human industries and impacts much of modern life. For instance, it is a major component of glass, concrete, and cements of many kinds. In addition, one of its most valuable applications lies in that it forms the fundamental substrate in manufacturing electronics devices such as integrated circuits and power transistors. Further, the element and its compounds find widespread use in explosives and pyrotechnics. Silicon is also used in mechanical seals, caulking compounds, and high-temperature, silicon-based greases.
The largest application of pure (metallurgical grade) silicon is in aluminum-silicon alloys, often called "light alloys," to produce cast parts, mainly for automotive industry. (This represents about 55% of the world consumption of pure silicon.)
The second largest application of pure silicon is as a raw material in the production of silicones (about 40% of the world consumption of silicon)
Pure silicon is also used to produce ultra-pure silicon for electronic and photovoltaic applications:
Ultrapure silicon can be doped with other elements to adjust its electrical response by controlling the number and charge (positive or negative) of current carriers. Such control is necessary for transistors, solar cells, microprocessors, semiconductor detectors and other semiconductor devices which are used in electronics and other high-tech applications. Hydrogenated amorphous silicon is widely used in the production of low-cost, large-area electronics in applications such as LCDs. It has also shown promise for large-area, low-cost thin-film solar cells.
Silicon dioxide or silica in the form of sand and clay is an important ingredient of concrete and brick and is also used to produce Portland cement. Silica from sand is a principal component of glass. Glass can be made into a great variety of shapes and with a many different physical properties. Silica is used as a base material to make window glass, containers, insulators, and many other useful objects. Silicon carbide is one of the most important abrasives. Silicones are flexible compounds containing silicon-oxygen and silicon-carbon bonds; they are widely used in applications such as artificial breast implants and contact lenses. Silicones are also used in many other applications. Silly Putty was originally made by adding boric acid to silicone oil. Now name-brand Silly Putty also contains significant amounts of elemental silicon, silicon binds to the silicone and allows the material to bounce 20 percent higher.
Silicon-based life
Given that silicon is similar to carbon, particularly in its valency, some have pondered over the possibility of silicon-based life. For instance, A. G. Cairns-Smith has proposed that the first living organisms may have been forms of clay minerals, which were probably based around the silicon atom.
Although there are no known forms of life that rely entirely on silicon-based chemistry, there are some that rely on silicon minerals for specific functions. Some bacteria and other forms of life, such as the protozoa radiolaria, have silicon dioxide skeletons, and the sea urchin has spines made of silicon dioxide. These forms of silicon dioxide are known as biogenic silica. Silicate bacteria use silicates in their metabolism.
Yet, life as it is known today could not have developed based on a silicon biochemistry. The main reason is that life on Earth depends on the carbon cycle: Autotrophic organisms use carbon dioxide to synthesize organic compounds with carbon, which is then used as food by heterotrophic organisms, which produce energy and carbon dioxide from these compounds. If carbon were to be replaced by silicon, there would be a need for a silicon cycle, involving the participation of silicon dioxide. However, unlike carbon dioxide, silicon dioxide is a solid that does not dissolve in water and cannot be transported through living systems by common biological means. Consequently, another solvent would be necessary to sustain silicon-based life forms. It would be difficult (if not impossible) to find another common compound with the unusual properties of water that make it an ideal solvent for carbon-based life.
Larger silicon compounds (silanes) that are analogous to common hydrocarbon chains are generally unstable, owing to the larger atomic radius of silicon and the correspondingly weaker silicon-silicon bond. Silanes decompose readily and often violently in the presence of oxygen, making them unsuitable for an oxidizing atmosphere such as our own. Moreover, unlike carbon, silicon does not have the tendency to form double and triple bonds.
Some silicon rings (cyclosilanes) have been synthesized and are analogous to the cycloalkanes formed by carbon, but the cyclosilanes are rare whereas the cycloalkanes are common. Synthesis of the cyclosilanes suffers from the difficulties inherent in producing any silane compound. On the other hand, carbon will readily form five-, six-, and seven-membered rings by a variety of pathways, even in the presence of oxygen.
Silicon's inability to readily form multiple bonds, long silane chains, and rings severely limits the diversity of compounds that can be synthesized from it. Under known conditions, silicon chemistry simply cannot begin to approach the diversity of organic chemistry, a crucial factor in carbon's role in biology.
Some have construed silicon-based life as existing under a computational substrate. This concept, yet to be explored in mainstream technology, receives ample coverage by science fiction authors.
Ponder this
Why is the Earth's crust consists of mainly silicon-based compounds?
If silicon is the most abundant element on Earth, why does the organic cycle on the planet carbon-based rather than silicon-based?
Discuss
Compare and contract between carbon and silicon. What are their similarities in terms of physical characteristics, chemical attributes, caomparable compounds. Can we substitute one for the other in all cases? How would an organic compound (such as petrochemicals, sugars, lipids) look if they are silicon-based instead? Would they have the same characteristics and serve the same function in nature?
Further readings
Silicon, from the Periodic Table of Videos brought to you by the University of Nottingham.
Monocrystalline silicon, used in semiconductors.
Amorphous silicon and polycrystalline silicon, both used in solar cells and LCDs.
Organosilicon, possible chemical basis for silicon-based lifeforms.