Important Compounds of Silicon

Silicon is an element with an atomic number 14 and the symbol Si. In 1823, Berzelius discovered Silicon. It is a tetravalent metalloid and semiconductor that is a hard, brittle crystalline solid with a blue-grey metallic lustre. Silicon belongs to the periodic table’s 14th group (carbon family).

Silicon is found in various materials such as dust, sand, clay, stone, silica and silicate minerals. Silicon is the eighth-most abundant element in the universe by mass, and it doesn’t occur in a pure state. The most important compounds of silicons in the earth’s crust are silica and silicates (around 95%). 

Properties of Silicon

1. Atomic number- 14
2. Atomic weight- 28.09
3. Electronic configuration- [Ne] 3S23P2
4. Covalent radius- 118
5. Ionic radius M4+/pmb- 40
6. Ionisation enthalpy/kJ mol-1
7. ∆iH1- 786
8. ∆iH2- 1577
9. ∆iH3- 3228
10. ∆iH4- 4354
11. Electronegativity- 1.8
12. Density/g cm–³- 2.34
13. Melting point/K- 1693
14. Boiling point/K- 3550
15. Electrical resistivity/ohm-cm- 50
16. It is strong, delicate and breakable and brittle
17. Colour- green, shiny, metallic colour
18. It is a semiconductor.

Uses of Silicon

• Ceramics and bricks are made of Silicon.
• This element is used to make transistors due to its semiconductivity property.
• Silicon is employed in various products such as computer processors and solar cells.
• It is an important constituent of Portland cement.
• Silicon is used in the manufacture of fire bricks.
• Silicones are used in a variety of waterproofing methods.
• It is also a component of ferrosilicon (an alloy), frequently used in the steel industry.

Important Compounds of Silicon

The various important compounds of Silicon are

• Silicon dioxide
• Silicones
• Silicates
• Zeolites

Silicon Dioxide, SiO2

Silicon dioxide (SiO2) is often known as Silica and exists in a variety of crystallographic forms. Quartz, cristobalite, and tridymite are crystalline forms of silica that are interconvertible when heated to a certain temperature. Silicon dioxide is a tetrahedrally connected covalent molecule with four oxygen atoms.

Each oxygen atom then forms a covalent link with a silicon atom. Each tetrahedron shares a corner with another tetrahedron. The entire crystal can be thought of as a large molecule made up of eight-membered rings.

Silica is almost non-reactive due to its high Si—O bond enthalpy. It doesn’t react with halogens, dihydrogen, metals, and most of the acids at high temperatures. However, it reacts with HF and NaOH.

SiO2 + 2 NaOH → Na2SiO3 + H2O

SiO2 + 4 HF → SiF4 + 2H2O

Quartz is extensively used as a piezoelectric material. Quartz is mainly used to manufacture accurate clocks, modern radio and television broadcasting and mobile radio communications.

Properties of Silicon dioxide

• Molecular formula- SiO2
• Molecular weight- 60
• It has high melting and boiling point
• It is amorphous in nature.
• It is insoluble in water
• It is non-volatile in nature.
• It doesn’t conduct electricity.

Uses of Silicon Dioxide

• Silicon dioxide is mainly used as a drying agent.
• Silica gel is also supported by chromatographic materials and catalysts. 
• Fumed silica is a type of Silicon dioxide used as an antiaging agent.
• Due to its high melting point, silica can be utilised in applications like iron casting and modern sand casting.
• In the hydraulic fracturing of tight oil, crystalline silica is used.
• In the filtering plants, Kieselguhr, an amorphous type of Silica, is used.

Silicones

Silicones are organosilicon polymers that have a repeating unit (R2SiO). The starting components for the production of Silicones are alkyl or aryl-substituted silicon chlorides (RnSiCl(4–n), where R is an alkyl or aryl group).

Formation of silicones: Methyl chloride reacts with Silicon in the presence of copper (catalyst) at 573K to form methyl-substituted chlorosilanes like MeSiCl3, Me2SiCl2, and Me3SiCl. Hydrolysis of dimethyldichlorosilane (CH3)2SiCl2 followed by condensation polymerisation yields a straight-chain polymer which is known as silicone.

Properties of Silicones

• Silicones contain non-polar alkyl groups, so they are water-repelling in nature.
• They have high thermal stability and dielectric strength.
• They are resistant to oxidation and chemicals.

Uses of Silicones

• They are used as sealant, greases, electrical insulators and for waterproofing of fabrics. 
• They are also used in surgical and cosmetic plants as they are incompatible in nature.

Silicates

SiO4 is the fundamental structural unit of silicates, consisting of a silicon atom coupled to four oxygen atoms in a tetrahedral arrangement. The discrete unit or a group of such units are connected together via corners in silicates by sharing 1, 2, 3, or 4 oxygen atoms per silicate unit. Chain, ring, sheet, or three-dimensional structures are formed when silicate units are connected together.

Positively charged metal ions counteract the negative charge on the silicate structure. A three-dimensional network is generated when all four corners are shared with other tetrahedral units. Glass and cement are man-made silicates.

Properties of Silicates

• Solid silicates are often well defined and stable. 
• Silicates containing alkali cations and tiny or chain-like anions, such as sodium ortho- and metasilicate, are slightly soluble in water. 
• When they are crystallised, they generate numerous solid hydrates.

Uses of Silicates

• They are mainly used in the preparation of Glass and ceramic.
• Silicate ceramic tiles are used on the space shuttle to protect them from the high atmospheric temperature.

Zeolites

Zeolites are aluminosilicates of microporous solids known as molecular sieves. If aluminium atoms replace a few silicon atoms in a 3D network of silicon dioxide, the overall structure known as aluminosilicate acquires a negative charge. Cations such as Na+, K+ or Ca2+ balance the negative charge.

Natural Zeolites are obtained from volcanic rocks and ash layers when they react with alkaline groundwater. In shallow marine basins, Zeolites crystallise in post-depositional conditions for periods ranging from thousands to millions of years. Natural zeolites are rarely pure and are frequently polluted with other minerals, metals, quartz, or other zeolites to variable degrees.

Properties of Zeolites

• It is non-corrosive in nature
• It has high hydrothermal stability
• It environmentally harmless
• It has a high surface area

Uses of Zeolites

• Zeolites are widely used in petrochemical industries for the cracking of hydrocarbons as a catalyst.
• Alcohols directly into gasoline with the help of ZSM-5 (a type of zeolite)
• Hydrated zeolites are used in ion-exchange methods.

Conclusion

Silicon is probably one of the most important elements on earth, and we often come across it every now and then. Many advancements are being made day by day, and newer compounds are being discovered. However, the silicon compounds mentioned above are considered to be important and also have a wide range of applications.

We have given all the necessary info about these compounds of silicon. And hope that this was helpful in understanding the different compounds of silicon, their structure, properties, and also uses.