Silicon in the Earth

Protonation of silicon monoxide can in principle give rise to two different isomers the O-protonated SiOH+ and the silicon-protonated form HSiO+. SiOH+ is formed upon reaction of water with silicon cations200 and is believed to play a key role in the depletion mechanism of atomic silicon in the earth s ionosphere50. Theory (MP4) predicts the two cationic isomers to be separated by a substantial barrier of 91.5 kcalmol-1 (with respect to the formation of HSiO+ from SiOH+)193. The neutral counterpart SiOH" has been generated in a NR experiment from the cationic precursor (equation 28)193,201 (accessible via electron impact ionization of tetramethoxysilane). Neutral HSiO —in line with theoretical predictions202,203 —was successfully generated via Charge-Reversal NRMS... 

Aluminum is the most abundant metal and the third most abundant element, after oxygen and silicon, in the earth s crust. It is widely distributed and constitutes approximately 8 percent of the earth s surface layer. However, aluminum is a very reactive element and is never found as the free metal in nature. It is found combined with other elements, most commonly with oxygen, silicon, and fluorine. These chemical compounds are commonly found in soil, minerals (e.g., sapphires, rubies, turquoise), rocks (especially igneous rocks), and clays. These are the natural... 

In the same way that esters form the most important group of organic phosphorus compounds, compounds containing P-O-X linkages are at present the most prominent among those in group (b) above. In spite of the formal periodic relationship of silicon to carbon, and the relative abundance of silicon in the earth s crust, there is as yet little evidence that compounds with P-O-Si (or P-Si) linkages are involved on any major scale in life processes. ... 

Exposure to silicaceous dusts is a major occupational health concern in numerons industries. Much of the silicon in the earth is combined with other elements to form silicates. Various anions and cations are substitnted into the crystalline silica matrix. Minerals such as kaolin, an aluminum silicate, and talc, a magnesium silicate, are silicate minerals that are used in their pnre form. Many minerals of commercial importance are composed of mixtures of silica and silicates, such as feldspar and muscovite, in an infinite range of combinations. The pulmonary disease associated with silica exposure is greatly influenced by the silicate content of the material. It has been estimated that approximately 8.2 million workers in the United States are potentially exposed to crystalline silica dust each year. 

After oxygen, silicon is the most abundant element in the earth s crust, It occurs extensively as the oxide, silica, in various forms, for example, flint, quartz, sand, and as silicates in rocks and clays, but not as the free element, silicon. Silicon is prepared by reduction of silica, Si02- Powdered amorphous silicon can be obtained by heating dry powdered silica with either powdered magnesium or a... 

They are, potentially or actually, cheap. Most ceramics are compounds of oxygen, carbon or nitrogen with metals like aluminium or silicon all five are among the most plentiful and widespread elements in the Earth s crust. The processing costs may be high, but the ingredients are almost as cheap as dirt dirt, after all, is a ceramic. 

The nuclei of iron are especially stable, giving it a comparatively high cosmic abundance (Chap. 1, p. 11), and it is thought to be the main constituent of the earth s core (which has a radius of approximately 3500 km, i.e. 2150 miles) as well as being the major component of siderite meteorites. About 0.5% of the lunar soil is now known to be metallic iron and, since on average this soil is 10 m deep, there must be 10 tonnes of iron on the moon s surface. In the earth s crustal rocks (6.2%, i.e. 62000ppm) it is the fourth most abundant element (after oxygen, silicon and aluminium) and the second most abundant metal. It is also widely distributed. 

A photovoltaic cell (often called a solar cell) consists of layers of semiconductor materials with different electronic properties. In most of today s solar cells the semiconductor is silicon, an abundant element in the earth s crust. By doping (i.e., chemically introducing impurity elements) most of the silicon with boron to give it a positive or p-type electrical character, and doping a thin layer on the front of the cell with phosphorus to give it a negative or n-type character, a transition region between the two types... 

Silicon is the second most abundant element in the earth s crust. It occurs in sand as the dioxide Si02 and as complex silicate derivatives arising from combinations of the acidic oxide Si02 with various basic oxides such as CaO, MgO, and K20. The clays, micas, and granite, which make up most soils and rocks, are silicates. All have low solubility in water and they are difficult to dissolve, even in strong acids. Silicon is not found in the elemental state in nature. 

Oxygen and silicon are the most abundant elements in the earth s crust. Table 25-111 shows that 60% of the atoms are oxygen atoms and 20% are silicon atoms. If our sample included the oceans, hydrogen would move into the third place ahead of aluminum (remember that water contains two hydrogen atoms for every oxygen atom). If the sample included the central core... 

Aluminum is the most abundant metallic element in the Earth s crust and, after oxygen and silicon, the third most abundant element (see Fig. 14.1). However, the aluminum content in most minerals is low, and the commercial source of aluminum, bauxite, is a hydrated, impure oxide, Al203-xH20, where x can range from 1 to 3. Bauxite ore, which is red from the iron oxides that it contains (Fig. 14.23), is processed to obtain alumina, A1203, in the Bayer process. In this process, the ore is first treated with aqueous sodium hydroxide, which dissolves the amphoteric alumina as the aluminate ion, Al(OH)4 (aq). Carbon dioxide is then bubbled through the solution to remove OH ions as HCO and to convert some of the aluminate ions into aluminum hydroxide, which precipitates. The aluminum hydroxide is removed and dehydrated to the oxide by heating to 1200°C. 

Silicon is the second most abundant element in the Earth s crust. It occurs widely in rocks as silicates, compounds containing the silicate ion, Si032, and as the silica, Si02, of sand (Fig. 14.33). Pure silicon is obtained from quartzite, a granular form of quartz (another solid phase of SiOz), bv reduction with high-purity carbon in an electric arc furnace ... 

As a result of its unique chemical and physical properties, silica gel is probably the most important single substance involved in liquid chromatography today. Without silica gel, it is doubtful whether HPLC could have evolved at all. Silica gel is an amorphous, highly porous, partially hydrated form of silica which is a substance made from the two most abundant elements in the earth s crust, silicon and oxygen. Silica, from which silica gel is manufactured, occurs naturally, either in conjunction with metal oxides in the form of silicates, such as clay or shale, or as free silica in the form of quartz, cristobalite or tridymite crystals. Quartz is sometimes found clear and colorless, but more often in an opaque form, frequently colored... 

As can be seen in Fig. 2-1 (abundance of elements), hydrogen and oxygen (along with carbon, magnesium, silicon, sulfur, and iron) are particularly abundant in the solar system, probably because the common isotopic forms of the latter six elements have nuclear masses that are multiples of the helium (He) nucleus. Oxygen is present in the Earth s crust in an abundance that exceeds the amount required to form oxides of silicon, sulfur, and iron in the crust the excess oxygen occurs mostly as the volatiles CO2 and H2O. The CO2 now resides primarily in carbonate rocks whereas the H2O is almost all in the oceans. 

Compounds of silicon with oxygen are prevalent in the Earth s crust. About 95% of crastal rock and its various decomposition products (sand, clay, soil) are composed of silicon oxides. In fact, oxygen is the most abundant element in the Earth s crast (45% by mass) and silicon is second (27%). In the Earth s surface layer, four of every five atoms are silicon or oxygen. 

In the previous paragraph, it has been stated that minerals have the same structure but different compositions (phenomenon of isomorphism of minerals) while some minerals have the same composition but different structures (phenomenon of polymorphism of minerals). Mineral composition and structure are both important in studying and classifying minerals. The major class of minerals - based on composition and structure - include elements, sulfides, halides, carbonates, sulfates, oxides, phosphates, and silicates. The silicate class is especially important, because silicon makes up 95% of the minerals, by volume, in the Earth s crust. Mineral classes are divided into families on the basis of the chemicals in each mineral. Families, in turn, are made of groups of minerals that have a similar structure. Groups are further divided into species. 

Silicon is one of the most abundant elements in the earth s crust. We find silicon in sand and quartz, and in our NMR tubes. Of course we also find it in the computers which run our NMR spectrometers. 

The chemistry of carbon, known as organic chemistry, has i already been discussed. The element silicon, also in Group IV, is just as significant in the mineral world as carbon is in the world of living things. Silicon is the second most abundant element in the earth s crust (oxygen is the most abundant). 

Occurrence. Silicon is the second most abundant element in the earth s crust, after oxygen (about 28% by weight). It occurs mainly in oxides (quartz, agate, opal, etc.) and a great variety of silicate minerals (feldspar, clay, mica, olivine, etc.). 

We know a great deal about the nature of the universe. For instance, the element hydrogen makes up about 75% of all the mass in the universe. In terms of number, about 90% of all atoms in the universe are hydrogen atoms, and most of the rest of the atoms in the universe are helium. All the other heavier elements make up just one to two percent of the total. Interestingly, the most abundant element on Earth (in number of atoms) is oxygen (O ). Oxygen accounts for about 50% of all the elements found in the Earth s crust, and silicon, the second most abundant element, makes up about 25%. Silicon dioxide (SiO ) accounts for about 87% of the total Earth s mass. Sfiicon dioxide is the main chemical compound found in sand and rocks. 

Aluminum is the third most abundant element found in the Earths crust. It is found in concentrations of 83,200 ppm (parts-per-million) in the crust. Only the nonmetals oxygen and silicon are found in greater abundance. Aluminum oxide (Al Oj) is the fourth most abundant compound found on Earth, with a weight of 69,900 ppm. Another alum-type compound is potassium aluminum sulfate [KA1(S0 )2 12H20]. Although aluminum is not found in its free metalhc state, it is the most widely distributed metal (in compound form) on Earth. Aluminum is also the most abundant element found on the moon. 

ISOTOPES There are 21 isotopes of silicon, three of which are stable. The isotope Si-28 makes up 92.23% of the element s natural abundance in the Earth s crust, Si-29 constitutes 4.683% of all silicon found in nature, and the natural abundance of Si-30 is merely 3.087% of the stable silicon isotopes found in the Earth s crust. 

Silicon, in the form of silicon dioxide (SiO ), is the most abundant compound in the Earths crust. As an element, silicon is second to oxygen in its concentration on Earth, yet it is... 

Qualitatively and quantitatively, compounds of silicon and oxygen are the class of substances of greatest importance in the earth s crust and mantle, in regard to both mass and variety of structural forms. 

Silicon is the most abundant metal-like element in the earth s crust. It is seldom present in pure elemental form, but is rather found in a large number of polymers based largely on the polycondensation of the orthosilicate anion, SiO as illustrated in the following equations ... 

Feldspars are the most abundant minerals in the earth s crust, accounting for about 60% of all igneous rocks. They are derivatives of silica in which about one-half or one-quarter of the silicon atoms have been replaced by aluminum. Feldspar is used in the manufacture of certain types of glass and pottery. Some feldspar crystals, such as moonstone (white perthilte), Amazon stone (green microcline), and multicolored labradorite, are used as gem stones and in architectural decorations. Some are used as a coating and filler in the production of paper. 

Most of these are relatively common and some are common indeed. For example, silicon and aluminum are the second and third most abundant elements in the Earth s crust. The rarest of these elements, selenium, is twice as abundant as silver and 20 times more abundant than gold, and it is relatively easy to obtain because it often occurs in sulfur deposits. 

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