silicon - Purification, Different forms of silicon, Compounds

Si, element 14, melting point 1410°C. A grey solid non-metal, the second most common element in the crust of the Earth, 26% by weight. It is the second element in the carbon group, and like carbon it forms mainly covalent compounds, with a valence of 4. It does not occur uncombined in nature. In addition to a large number of minerals which are essentially SiO₂, it occurs in many alumino-silicates. Very pure silicon is widely used in electronic devices. It is also doped with controlled amounts of aluminium, phosphorus, and other elements to alter its conductivity. Silicates are the main constituents of brick, stone, cement, and glass.

aluminium ← silicon → phosphorus

C
↑
Si
↓
Ge

Periodic Table - Extended Periodic Table

General

Name, Symbol, Number

silicon, Si, 14

Chemical series

metalloids

Group, Period, Block

14, 3, p

Appearance

dark gray, bluish tinge

Atomic mass

28.0855(3) g/mol

Electron configuration

[Ne] 3s

Electrons per shell

2, 8, 4

Physical properties

Phase

solid

Density (near r.t.)

2.33 g·cm−3

Liquid density at m.p.

2.57 g·cm−3

Melting point

1687 K
(1414 °C, 2577 °F)

Boiling point

3538 K
(3265 °C, 5909 °F)

Heat of fusion

50.21 kJ·mol−1

Heat of vaporization

359 kJ·mol−1

Heat capacity

(25 °C) 19.789 J·mol

Vapor pressure

P/Pa	1	10	100	1 k	10 k	100 k
at T/K	1908	2102	2339	2636	3021	3537

Atomic properties

Crystal structure

Diamond Lattice

Oxidation states

4
(amphoteric oxide)

Electronegativity

1.90 (Pauling scale)

Ionization energies
(more)

1st: 786.5 kJ·mol−1

2nd: 1577.1 kJ·mol−1

3rd: 3231.6 kJ·mol−1

Atomic radius

110 pm

Atomic radius (calc.)

111 pm

Covalent radius

111 pm

Van der Waals radius

210 pm

Miscellaneous

Magnetic ordering

nonmagnetic

Thermal conductivity

(300 K) 149 W·m

Thermal expansion

(25 °C) 2.6 µm·m

Speed of sound (thin rod)

(20 °C) 8433 m/s

Young's modulus

47 GPa

Bulk modulus

100 GPa

Mohs hardness

6.5

CAS registry number

7440-21-3

Selected isotopes

Main article: Isotopes of silicon

iso	NA	half-life	DM	DE (MeV)	DP
28Si	92.23%	Si is stable with 14 neutrons
29Si	4.67%	Si is stable with 15 neutrons
30Si	3.1%	Si is stable with 16 neutrons
32Si	syn	132 y	β-	13.020	32P

References

Not to be confused with Silicone.

Silicon (IPA: /ˈsɪlikən/, Latin: silicium) is the chemical element in the periodic table that has the symbol Si and atomic number 14.

Silicon and alloys

The largest application of pure silicon (metallurgical grade silicon) is in aluminum - silicon alloys, often called "light alloys", to produce cast parts, mainly for automotive industry (this represents about 55% of the world consumption of pure silicon). The second largest application of pure silicon is as a raw material in the production of silicones (about 40% of the world consumption of silicon) Pure silicon is also used to produce ultrapure silicon for electronic and photovoltaic applications : Semiconductor - Ultrapure silicon can be doped with other elements to adjust its electrical response by controlling the number and charge (positive or negative) of current carriers.

Purification

The use of silicon in semiconductor devices demands a much greater purity than afforded by metallurgical grade silicon. The earliest method of silicon purification, first described in 1919 and used on a limited basis to make radar components during World War II, involved crushing metallurgical grade silicon and then partially dissolving the silicon powder in an acid.

In zone melting, also called zone refining, the first silicon purification method to be widely used industrially, rods of metallurgical grade silicon are heated to melt at one end.

Chemical methods

Today, silicon is instead purified by converting it to a silicon compound that can be more easily purified than silicon itself, and then converting that silicon element back into pure silicon.

At one time, DuPont produced ultrapure silicon by reacting silicon tetrachloride with high-purity zinc vapors at 950 °C, producing silicon according to the chemical equation

SiCl4 + 2 Zn → Si + 2 ZnCl2

However, this technique was plagued with practical problems (such as the zinc chloride byproduct solidifying and clogging lines) and was eventually abandoned in favor of the Siemens process.

Different forms of silicon

Granular silicon	Polycrystal silicon	Silicon monocrystal	Silicon nanopowder
Silicon Ingot

One can notice the color change in silicon nanopowder.

Compounds

For examples of silicon compounds see silicate, silane (SiH4), silicic acid (H4SiO4), silicon carbide (SiC), silicon dioxide (SiO2), silicon tetrachloride (SiCl4), silicon tetrafluoride (SiF4), and trichlorosilane (HSiCl3).