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14 Si 28.0855(3)

Silicon

Metalloid
Symbol Si
Atomic Number 14
Atomic Weight 28.0855(3)
CAS Registry ID 7440-21-3
Group Name (none)
Period Number 3
Block p-block
State at STP Solid

Description

Sample of Silicon ⌕ Enlarge Image

Silicon is a metalloid with an atomic weight of 28.0855. In its natural solid state, silicon is dark grey in color, it has a melting point of 2577 °F, and a boiling point of 5252 °F. Silicon makes up 25.7% of the Earth’s crust, and it is the second most abundant element on earth. Common uses of silicon include: as a component in glass, cement, and concrete, in the use of electronic circuit manufacture, as a component in explosives and fireworks, and in the production of silicones.

Isolation

Pure silicon does exist in nature in a crystalline form, but it is very rare. Isolation procedures are necessary to obtain enough high grade pure silicon for commercial purposes.

Silicon ⌕ Enlarge Image

There are a number of isolation methods that can be used to isolate pure silicon; which method that is used depends on what the silicon is going to be used for, and how pure it needs to be.

Large scale isolation of silicon to be used for commercial purposes is isolated from silica. Silca minerals such as sand, quartz, rock crystal, and agate, all contains high amounts of silicon dioxide in various crystalline forms. Through the isolation process, silica minerals that contain high purity silica are reacted with charcoal, coal, and wood in an electric arc furnace Carbon electrodes are used, and the furnace is heated to over 3452 °F. An electric arc furnace uses the electrical breakdown of gas through heat charged materials. Through the isolation process, liquid silicon is drained from the bottom of the furnace and then cooled. One another isolation reaction that results in pure silicon uses the reaction between silicon chloride with hydrogen.

General

NameSilicon
SymbolSi
Number14
Chemical seriesMetalloid
Group14
Period3
Blockp
Appearancedark grey with bluish tinge
Standard atomic weight28.0855(3) g·mol⁻¹
Electron configuration[Ne] 3s2 3p2
Electrons per shell2, 8, 4

Atomic Properties

Crystal structureDiamond
Oxidation states4 (amphoteric oxide)
Electronegativity1.90 (Pauling scale)
Ionization energies1st: 786.5 kJ·mol−1
2nd: 1577.1 kJ·mol−1
3rd: 3231.6 kJ·mol−1
Atomic radius117.6 pm
Atomic radius (calc.)111 pm
Covalent radius111 pm
Van der Waals radius210 pm

Physical Properties

Phasesolid
Density (near r.t.)2.33 g·cm−3
Liquid density at m.p.2.57 g·cm−3
Melting point1687 K (1414 °C, 2577 °F)
Boiling point3538 K (3265 °C, 5909 °F)
Critical point
Heat of fusion50.21 kJ·mol−1
Heat of vaporization359 kJ·mol−1
Heat capacity(25 °C) 19.789 J·mol−1·K−1

Miscellaneous

Magnetic orderingnonmagnetic
Electrical resistivity
Thermal conductivity(300 K) 149 W·m−1·K−1
Thermal expansion(25 °C) 2.6 µm·m−1·K−1
Speed of sound (thin rod)(20 °C) 8433 m/s
Young's modulus150 GPa
Shear modulus
Bulk modulus100 GPa
Poisson ratio
Mohs hardness6.5
Vickers hardness
Brinell hardness