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Nevertheless, even with these highly electropositive elements true silicon anions are not obtainable, and most of these compounds are semiconductors. Perfection Appliance Repair Withoutabox Submit to Film Festivals. Best Bed Bug Treatment. Best Kona Coffee Online.


10 Smoothies to Boost Your Pregnancy Glow

And the word citrine has me suspicious My stomach was acidy and upset the entire time which I would have tolerated had I seen results.

Also, had a bit of a headache very slight about an hour after I took these. It went away within a few hours, but annoying enough and seemed to coincide with taking it. I've given up on miracles. Eat less, exercise more. If it were so easy! Citrine provides a variety of ingredients see the "Supplement Facts" image on the product page for details , including mg of caffeine to keep you awake.

Citrine seemed to make me a bit more jittery than a different pill's mg of caffeine. Otherwise, I felt no discernible effects, good or bad. Be sure to drink plenty of water. At two a day, this bottle lasts about two months. If the price is right, go for it.

Having only used this for about 2 weeks, inconsistently, I can't speak much about weight management in numbers whether they be waist size or weight. Now that that part is out of the way I work really long days. Citrine helps keep focus and energy running, even on the days I'm running on little to no sleep. They do help on suppressing hunger. They DO NOT make you not hungry, but when eating, you will eat at far more moderate to low amounts if overeating is the issue, which is my tendency. When taking them on an empty stomach, I do get weird herbal mixed with citrusy burps for about 30 mins after taking them But even in the Texas late spring, it's not noticeable for more than an hour or so.

An added bonus is I have not noticed any jitteriness even with mg caffeine anhydrous, my preferred caffeine over the non-anhydrous variety. Over all, for focus and energy With the weight suppression, I can see them helping quite well with dieting and weight management. Once I begin back at the gym, I will edit and append my review to add bonus information.

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Amazon Rapids Fun stories for kids on the go. Amazon Restaurants Food delivery from local restaurants. Such use includes industrial construction with clays , silica sand , and stone. Silicates are used in Portland cement for mortar and stucco , and mixed with silica sand and gravel to make concrete for walkways, foundations, and roads. They are also used in whiteware ceramics such as porcelain , and in traditional quartz -based soda-lime glass and many other specialty glasses.

Silicon compounds such as silicon carbide are used as abrasives and components of high-strength ceramics. Silicon is the basis of the widely used synthetic polymers called silicones. Elemental silicon also has a large impact on the modern world economy. Most free silicon is used in the steel refining, aluminium -casting, and fine chemical industries often to make fumed silica. Silicon is an essential element in biology, although only traces are required by animals. However, various sea sponges and microorganisms, such as diatoms and radiolaria , secrete skeletal structures made of silica.

Silica is deposited in many plant tissues. In Antoine Lavoisier suspected that silica might be an oxide of a fundamental chemical element , [9] but the chemical affinity of silicon for oxygen is high enough that he had no means to reduce the oxide and isolate the element.

German Silizium , Turkish silisyum. A few others use instead a calque of the Latin root e. In , Gay-Lussac and Thénard are thought to have prepared impure amorphous silicon , through the heating of recently isolated potassium metal with silicon tetrafluoride , but they did not purify and characterize the product, nor identify it as a new element.

He retained part of Davy's name but added "-on" because he believed that silicon was a nonmetal similar to boron and carbon. Silicon in its more common crystalline form was not prepared until 31 years later, by Deville. Starting in the s, the work of William Lawrence Bragg on X-ray crystallography successfully elucidated the compositions of the silicates, which had previously been known from analytical chemistry but had not yet been understood, together with Linus Pauling 's development of crystal chemistry and Victor Goldschmidt 's development of geochemistry.

The middle of the 20th century saw the development of the chemistry and industrial use of siloxanes and the growing use of silicone polymers , elastomers , and resins. In the late 20th century, the complexity of the crystal chemistry of silicides was mapped, along with the solid-state chemistry of doped semiconductors. Because silicon is an important element in high-technology semiconductor devices, many places in the world bear its name.

For example, Santa Clara Valley in California acquired the nickname Silicon Valley since the element is the base material used in the semiconductor industry located there. Since then, many other locations have been nicknamed for similar reasons.

A silicon atom has fourteen electrons. In the ground state, they are arranged in the electron configuration [Ne]3s 2 3p 2. Of these, four are valence electrons , occupying the 3s orbital and two of the 3p orbitals. Like the other members of its group, the lighter carbon and the heavier germanium , tin , and lead , it has the same number of valence electrons as valence orbitals: Following periodic trends , its single-bond covalent radius of At standard temperature and pressure, silicon is a shiny semiconductor with a bluish-grey metallic lustre; as typical for semiconductors, its resistivity drops as temperature rises.

This arises because silicon has a small energy gap between its highest occupied energy levels the valence band and the lowest unoccupied ones the conduction band. The Fermi level is about halfway between the valence and conduction bands and is the energy at which a state is as likely to be occupied by an electron as not.

Hence pure silicon is an insulator at room temperature. However, doping silicon with a pnictogen such as phosphorus , arsenic , or antimony introduces one extra electron per dopant and these may then be excited into the conduction band either thermally or photolytically, creating an n-type semiconductor.

Similarly, doping silicon with a group 13 element such as boron , aluminium , or gallium results in the introduction of acceptor levels that trap electrons that may be excited from the filled valence band, creating a p-type semiconductor.

Joining n-type silicon to p-type silicon creates a p-n junction with a common Fermi level; electrons flow from n to p, while holes flow from p to n, creating a voltage drop. This p-n junction thus acts as a diode that can rectify alternating current that allows current to pass more easily one way than the other.

A transistor is an n-p-n junction, with a thin layer of weakly p-type silicon between two n-type regions. Biasing the emitter through a small forward voltage and the collector through a large reverse voltage allows the transistor to act as a triode amplifier. Silicon crystallises in a giant covalent structure at standard conditions, specifically in a diamond cubic lattice. It is not known to have any allotropes at standard pressure, but several other crystal structures are known at higher pressures.

Naturally occurring silicon is composed of three stable isotopes , 28 Si The fusion of 28 Si with alpha particles by photodisintegration rearrangement in stars is known as the silicon-burning process ; it is the last stage of stellar nucleosynthesis before the rapid collapse and violent explosion of the star in question in a type II supernova. The known isotopes of silicon range in mass number from 22 to Crystalline bulk silicon is rather inert, but becomes more reactive at high temperatures.

Like its neighbour aluminium, silicon forms a thin, continuous surface layer of silicon dioxide SiO 2 that protects the metal from oxidation. Silicon does not react with most aqueous acids, but is oxidised and fluorinated by a mixture of concentrated nitric acid and hydrofluoric acid ; it readily dissolves in hot aqueous alkali to form silicates.

At high temperatures, silicon also reacts with alkyl halides ; this reaction can be catalysed by copper to directly synthesise organosilicon chlorides as precursors to silicone polymers. Upon melting, silicon becomes extremely reactive, alloying with most metals to form silicides , and reducing most metal oxides because the heat of formation of silicon dioxide is so large.

As a result, containers for liquid silicon must be made of refractory , unreactive materials such as zirconium dioxide or group 4, 5, and 6 borides.

Tetrahedral coordination is a major structural motif in silicon chemistry just as it is for carbon chemistry. However, the 3p subshell is rather more diffuse than the 2p subshell and does not hybridise as well with the 3s subshell. As a result, the chemistry of silicon and its heavier congeners shows significant differences from that of carbon, [32] and thus octahedral coordination is also significant. The poor overlap of 3p orbitals also results in a much lower tendency towards catenation formation of Si—Si bonds for silicon than for carbon due to the concomitant weakening of the Si—Si bond compared to the C—C bond: Silicon already shows some incipient metallic behaviour, particularly in the behaviour of its oxide compounds and its reaction with acids as well as bases though this takes some effort , and is hence often referred to as a metalloid rather than a nonmetal.

Silicon shows clear differences with carbon. For example, organic chemistry has very few analogies with silicon chemistry, while silicate minerals have a structural complexity unseen in oxocarbons.

Additionally, the lower Ge—O bond strength compared to the Si—O bond strength results in the absence of "germanone" polymers that would be analogous to silicone polymers. Many metal silicides are known, most of which have formulae that cannot be explained through simple appeals to valence: They are structurally more similar to the borides than the carbides , in keeping with the diagonal relationship between boron and silicon, although the larger size of silicon than boron means that exact structural analogies are few and far between.

The heats of formation of the silicides are usually similar to those of the borides and carbides of the same elements, but they usually melt at lower temperatures. Except for copper , the metals in groups 11—15 do not form silicides. Most instead form eutectic mixtures , although the heaviest post-transition metals mercury , thallium , lead , and bismuth are completely immiscible with liquid silicon.

Silicides are usually prepared by direct reaction of the elements. For example, the alkali metals and alkaline earth metals react with silicon or silicon oxide to give silicides. Nevertheless, even with these highly electropositive elements true silicon anions are not obtainable, and most of these compounds are semiconductors. Cu 5 Si ; with increasing silicon content, catenation increases, resulting in isolated clusters of two e. U 3 Si 2 or four silicon atoms e.

CaSi , layers e. CaSi 2 , or three-dimensional networks of silicon atoms spanning space e. The silicides of the group 1 and 2 metals are usually more reactive than the transition metal silicides. The latter usually do not react with aqueous reagents, except for hydrofluoric acid ; however, they do react with much more aggressive reagents like liquid potassium hydroxide , or gaseous fluorine or chlorine when red-hot. The pre-transition metal silicides instead readily react with water and aqueous acids, usually producing hydrogen or silanes: Products often vary with the stoichiometry of the silicide reactant.

For example, Ca 2 Si is polar and non-conducting and has the anti-PbCl 2 structure with single isolated silicon atoms, and reacts with water to produce calcium hydroxide , hydrated silicon dioxide, and hydrogen gas.

CaSi with its zigzag chains of silicon atoms instead reacts to give silanes and polymeric SiH 2 , while CaSi 2 with its puckered layers of silicon atoms does not react with water, but will react with dilute hydrochloric acid: Speculation on silicon hydride chemistry started from the s, contemporary with the development of synthetic organic chemistry.

Silane itself, as well as trichlorosilane , were first synthesised by Friedrich Wöhler and Heinrich Buff in by reacting aluminium—silicon alloys with hydrochloric acid , and characterised as SiH 4 and SiHCl 3 by Charles Friedel and Albert Ladenburg in Disilane Si 2 H 6 followed in , when it was first made by Henri Moissan and Samuel Smiles by the protonolysis of magnesium silicides.

Further investigation had to wait until because of the great reactivity and thermal instability of the silanes; it was then that Alfred Stock began the study of silicon hydrides in earnest with new greaseless vacuum techniques, as they were found as contaminants of his focus, the boron hydrides.

The names silanes and boranes are due to him, based on analogy with the alkanes. Direct reaction of HX or RX with silicon, possibly with a catalyst such as copper, is also a viable method to produce substituted silanes.

They are all strong reducing agents. The first two, silane and disilane, are colourless gases; the heavier members of the series are volatile liquids. All silanes are very reactive and catch fire or explode spontaneously in air. They become less thermally stable with room temperature, so that only silane is indefinitely stable at room temperature, although disilane does not decompose very quickly only 2. They are much more reactive than the corresponding alkanes, because the larger radius of silicon compared to carbon facilitates nucleophilic attack at the silicon, the greater polarity of the Si—H bond compared to the C—H bond, and the ability of silicon to expand its octet and hence form adducts and lower the reaction's activation energy.

Silane pyrolysis gives polymeric species and finally elemental silicon and hydrogen; indeed ultrapure silicon is commercially produced by the pyrolysis of silane.

While the thermal decomposition of alkanes starts by the breaking of a C—H or C—C bond and the formation of radical intermediates, polysilanes decompose by eliminating silenes: While pure silanes do not react with pure water or dilute acids, traces of alkali catalyse immediate hydrolysis to hydrated silicon dioxide. The Si—H bond also adds to alkenes , a reaction which proceeds slowly and speeds up with increasing substitution of the silane involved.

The monohalosilanes may be formed by reacting silane with the appropriate hydrogen halide with an Al 2 X 6 catalyst, or by reacting silane with a solid silver halide in a heated flow reactor: Among the derivatives of silane, iodosilane SiH 3 I and potassium silanide KSiH 3 are very useful synthetic intermediates in the production of more complicated silicon-containing compounds: Silicon and silicon carbide readily react with all four stable halogens, forming the colourless, reactive and volatile silicon tetrahalides.

The melting and boiling points of these species usually rise with increasing atomic weight, though there are many exceptions: While catenation in carbon compounds is maximised in the hydrogen compounds rather than the halides, the opposite is true for silicon, so that the halopolysilanes are known up to at least Si 14 F 30 , Si 6 Cl 14 , and Si 4 Br These halopolysilanes may be produced by comproportionation of silicon tetrahalides with elemental silicon, or by condensation of lighter halopolysilanes trimethylammonium being a useful catalyst for this reaction.

Silicon dioxide SiO 2 , also known as silica, is one of the most well-studied compounds, second only to water. It is also known to occur pure as rock crystal ; impure forms are known as rose quartz , smoky quartz , morion , amethyst , and citrine. Some poorly crystalline forms of quartz are also known, such as chalcedony , chrysoprase , carnelian , agate , onyx , jasper , heliotrope , and flint. Other modifications of silicon dioxide are known in some other minerals such as tridymite and cristobalite , as well as the much less common coesite and stishovite.

Biologically generated forms are also known as kieselguhr and diatomaceous earth. Vitreous silicon dioxide is known as tektites , and obsidian , and rarely as lechatelierite. Seat Cover for Cars. Sound system for houses of worship. Top Star Reviews By Consumers.

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