Silicon is also used in the synthesis of polymers called silicones. Silicon does not occur as a free element in nature. It always occurs as a mineral with a combination of other elements. Silica is a compound made out of silicon and oxygen atoms.
Silica is the name given for silicon dioxide. The molecular formula of silica is SiO 2. Therefore, silica is made out of two most abundant elements on earth. Silica is found as quartz in nature. Silica is also the major constituent of sand. Under normal temperature and pressure, silica is a solid. Pure silica is a colorless crystalline compound having a high melting point.
The melting point of silica is about o C. Silica is obtained mostly by mining of quartz. Although silica is called silicon dioxide, the crystalline structure of silica shows that silicon atom is surrounded by four oxygen atoms attached through single covalent bonds. Elemental silicon is a major player in modern electronics because it's an ideal semiconductor of electricity.
When heated into a molten state, silicon can be formed into semi-conductive wafers, to serve as the base for integrated circuits microchips. In fact, Silicon Valley, the southern region of the San Francisco Bay Area, earned its name due to the high concentration of computer and electronics companies in the area producing silicon-based semiconductors and chips. Silicone, by contrast, is a synthetic polymer made up of silicon, oxygen and other elements, most typically carbon and hydrogen.
Silicone is generally a liquid or a flexible, rubberlike plastic, and has a number of useful properties, such as low toxicity and high heat resistance. It also provides good electrical insulation.
Materials containing these long chain silicates are called inosilicates "sinew" or "string" silicates. The polyhedral drawing of a section of inosilicate ion is shown below. Inosilicates are not exactly network solids because they do not form three-dimensional networks. However, at least in one direction, they are covalently bonded and can extend indefinitely. There could be hundreds of silicate units in a row. In a sense, inosilicates could also be described as polymers.
They contain individual units that keep repeating all along the chain. In the polyhedral drawing, the repeating units are simply tetrahedra. The inosilicate chain drawn above does illustrate an important consideration that it has in common with network solids. All network solids are different on the inside than they are on the outside. We can illustrate that difference in the inosilicate chain because it is a relatively simple structure.
In the inosilicate chain, each tetrahedron along the chain looks just like the next, but the ones on the end are different. They are only attached to one neighbor, not two. Compared to the other repeating units, these ones will have an extra oxygen with a negative charge. Extending that idea to network solids, in which the covalent bonds extend in three directions, we will encounter a similar problem as we move out from the center of the solid and we reach the surface.
The structure at the surface will be different from the structure in the interior of the solid, because we will run out atoms to keep connecting to. One of the most important inosilicates is wollastonite, which is used in a number of industries. It is added to ceramic tiles, paints and plastics, partly because it increases their durability and strength.
It is sometimes used to make brake pads for cars; it provides friction when pressed against the rotor, slowing down the wheels on your car, but because of its durability it does not wear out too quickly. Convert the polyhedral drawing of inosilicate ion into a Lewis structure. You can stop after five repeating units. Looking at the Lewis structure for inosilicate ion, how many calcium ions would accompany each repeating unit in Wollastonite?
In your Lewis structure for inosilicate ion, circle the repeat units. Propose a formula for Wollastonite. If silicate units can form chains, it shouldn't be a surprise that they can form other shapes, too. For example, the silicate units can wrap around to form rings. They come in a veriety of different sizes. These types of silicates are called cyclosilicates "wheel" silicates.
On of the most familar cyclosilicate mineral groups is the beryl family. The most prominent member of the family is emerald. It contains the cyclic anion shown below. All beryls have the same cyclosilicate anion. They even have the same counterions, with the general formula Be 3 Al 2 Si 6 O However, beryls come in different colors because of small amounts of cation impurities.
In emerald, a tiny amount of chromium ion provides the green color. The California state gem, benitoite, contains a cyclosilicate anion with just three silicon atoms in it.
Clearly we have turned back from the edge of network solids again. These anions may be large, but they certainly don't extend on and on in any direction.
However, previously, we looked at single unit silicates and extended them to doubles, then linked them together to make longer chains. What would happen if we could link some cyclosilicates together? The name "phyllosilicates" means, roughly, "leaf"-silicates.
These anions are sheets or leaves in which silicates link together to make two-dimensional networks. The structure shown below would extend on and on through the top, bottom and sides of the page or the screen.
The most familiar examples of phyllosilicates are the mica family. If you have ever seen mica, with its thin sheets, you can easily imagine how it would be composed of two-dimensional networks like the one above.
One of the most interesting applications of mica was its use as "Muscovy glass" in the old days in Russia. Its thin, transparent layers made very good windows. Micas are a slightly more complicated example of phyllosilicates because they are also aluminosilicates. A nonmetallic element symbol Si with an atomic number of 14 and atomic weight of Silicon dioxide, SiO. It constitutes ordinary quartz also opal and tridymite , and is artifically prepared as a very fine, white, tasteless, inodorous powder.
A nonmetalic element analogous to carbon. It always occurs combined in nature, and is artificially obtained in the free state, usually as a dark brown amorphous powder, or as a dark crystalline substance with a meetallic luster. Its oxide is silica, or common quartz, and in this form, or as silicates, it is, next to oxygen, the most abundant element of the earth's crust.
Silicon is characteristically the element of the mineral kingdom, as carbon is of the organic world. Symbol Si. Atomic weight Called also silicium. Silicon is a chemical element with the symbol Si and atomic number It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid and semiconductor.
Published: 15 Dec, Silica noun Silicon dioxide. Silicon noun A nonmetallic element symbol Si with an atomic number of 14 and atomic weight of Silica noun Any of the silica group of the silicate minerals.
Silicon noun A single atom of this element. Silica noun Silicon dioxide, SiO. Silicon noun slang computing. Silica noun a white or colorless vitreous insoluble solid SiO2 ; various forms occur widely in the earth's crust as quartz or cristobalite or tridymite or lechartelierite.
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