Silicon Facts

Silicon Chemical & Physical Properties

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Silicon Basic Facts

Symbol: Si

Atomic Weight: 28.0855

Discovery: Jons Jacob Berzelius 1824 (Sweden)

Word Origin: Latin: silicis, silex: flint

Properties: The melting point of silicon is 1410°C, boiling point is 2355°C, specific gravity is 2.33 (25°C), with a valence of 4. Crystalline silicon has a metallic grayish color. Silicon is relatively inert, but it is attacked by dilute alkali and by halogens. Silicon transmits over 95% of all infrared wavelengths (1.3-6.7 mm).

Uses: Silicon is one of the most widely used elements. Silicon is important to plant and animal life. Diatoms extract silica from water to build their cell walls. Silica is found in plant ashes and in the human skeleton. Silicon is an important ingredient in steel. Silicon carbide is an important abrasive and is used in lasers to produce coherent light at 456.0 nm. Silicon doped with gallium, arsenic, boron, etc. is used to produce transistors, solar cells, rectifiers, and other important solid-state electronic devices. Silicones range from liquids to hard solids and have many useful properties, including use as adhesives, sealants, and insulators. Sand and clay are used to make building materials. Silica is used to make glass, which has many useful mechanical, electrical, optical, and thermal properties.

Sources: Silicon makes up 25.7% of the earth's crust, by weight, making it the second most abundant element (exceeded by oxygen). Silicon is found in the sun and stars. It is a principal component of the class of meteorites known as aerolites. Silicon is also a component of tektites, a natural glass of uncertain origin. Silicon is not found free in nature. It commonly occurs as the oxide and silicates, including sand, quartz, amethyst, agate, flint, jasper, opal, and citrine. Silicate minerals include granite, hornblende, feldspar, mica, clay, and asbestos.

Preparation: Silicon may be prepared by heating silica and carbon in an electric furnace, using carbon electrodes. Amorphous silicon may be prepared as a brown powder, which can then be melted or vaporized. The Czochralski process is used to produce single crystals of silicon for solid-state and semiconductor devices. Hyperpure silicon may be prepared by a vacuum float zone process and by thermal decompositions of ultra-pure trichlorosilane in an atmosphere of hydrogen.

Element Classification: Semimetallic

Isotopes: There are known isotopes of silicon ranging from Si-22 to Si-44. There are three stable isotopes: Al-28, Al-29, Al-30.

Silicon Physical Data

Density (g/cc): 2.33

Melting Point (K): 1683

Boiling Point (K): 2628

Appearance: Amorphous form is brown powder; crystalline form has a gray

Atomic Radius (pm): 132

Atomic Volume (cc/mol): 12.1

Covalent Radius (pm): 111

Ionic Radius: 42 (+4e) 271 (-4e)

Specific Heat (@20°C J/g mol): 0.703

Fusion Heat (kJ/mol): 50.6

Evaporation Heat (kJ/mol): 383

Debye Temperature (K): 625.00

Pauling Negativity Number: 1.90

First Ionizing Energy (kJ/mol): 786.0

Lattice Structure: Diagonal

Lattice Constant (Å): 5.430

CAS Registry Number: 7440-21-3

Silicon Trivia:

  • Silicon is the eighth most abundant element in the universe.
  • Silicon crystals for electronics must have a purity of one billion atoms for every non-silicon atom (99.9999999% pure).
  • The most common form of silicon in the Earth's crust is silicon dioxide in the form of sand or quartz.
  • Silicon, like water, expands as it changes from liquid to solid.
  • Silicon oxide crystals in the form of quartz are piezoelectric. The resonance frequency of quartz is used in many precision timepieces.

References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952), CRC Handbook of Chemistry & Physics (18th Ed.) International Atomic Energy Agency ENSDF database (Oct 2010)

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