Atomic number 14

Silicon

Si
+ phase
− phase

Shells Orbitals 3s 3p

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14 electrons in 3 shells: 2, 8, 4.

Shells are a teaching model: an electron does not travel on a ring at a fixed distance.

Category: Metalloid
Period: 3
Group: 14
Block: p
Standard atomic weight: 28.085(1) Da
Electron configuration: [Ne] 3s² 3p²
Phase at 25 °C: solid
Melting point: 1414 °C
Boiling point: 3265 °C
Density: 2.3296 g/cm³
Electronegativity (Pauling): 1.9
Discovered: 1824, Jöns Jacob Berzelius

Neighbours in the table

Al P

Silicon sits directly below carbon in group 14, and its outer shell repeats carbon’s pattern one row down. A neon core then 3s² 3p² gives fourteen electrons, in shells of 2, 8 and 4. Four outer electrons are four short of an octet, the eight that complete a shell, and the atom makes up the difference by sharing in four covalent bonds. In silane, SiH₄, those four bonds go to four hydrogen atoms.

In the crystal each atom bonds instead to four silicon neighbours at the corners of a regular tetrahedron, the arrangement of diamond. A single crystal of silicon is one giant three-dimensional molecule. Melting such a covalent network solid means breaking covalent bonds, and since those bonds are strong the solid is hard and melts high, at 1414 °C. A second form, amorphous silicon, its atoms in no regular order, is a brown powder.

Silicon is a metalloid, an element whose properties fall between a metal’s and a nonmetal’s. The crystalline form is grey with a metallic lustre, yet it is a semiconductor. It conducts less well than a metal because its electrons are held more tightly by their nuclei. OpenStax traces this in-between behaviour partly to electronegativity, how strongly an atom pulls on the electrons in a bond. Silicon’s, 1.9 on the Pauling scale, sits in between.

Where it is found

Silicon never occurs free in nature. Los Alamos puts it at 25.7% of the crust’s weight, second only to oxygen, and PubChem’s element record adds 2.2 milligrams in every litre of sea water. Nearly all of it is bound to oxygen, as the oxide or as silicates. Sand, quartz, flint, agate, opal and amethyst are forms of the oxide; granite, feldspar, clay and mica are among the silicate minerals.

In those minerals each silicon atom sits at the centre of four oxygen atoms, a silicon-oxygen tetrahedron. The tetrahedra may stand alone or share corner oxygens in many patterns, joining into chains, layers and three-dimensional frameworks, and various positive ions pack between them. That freedom is why there are so many silicate minerals, the bulk of common rock, soil and clay.

The element is won from the oxide in an electric furnace. Silica is heated with carbon, using carbon electrodes, at close to 2200 °C; the carbon leaves as carbon monoxide and silicon remains. China made almost 80% of the world’s silicon materials in 2024, and the five plants in the United States all lie east of the Mississippi River.

Why it matters

OpenStax calls purified silicon the computer industry’s most important element. A semiconductor has a filled band of electron energies, an empty band above it and a small gap between them; silicon’s gap is 1.14 eV.

An arsenic atom in a silicon atom’s place brings five valence electrons, not four, and the fifth finds no room in the filled band. It rests 0.02 eV below the conduction band; room temperature easily excites it into that band to carry current. The carriers are negative electrons, so this is an n-type semiconductor. Aluminium, with three, leaves holes, empty states in the filled band that neighbouring electrons move into; those positive carriers make it p-type.

Chip-grade silicon holds no more than one part of impurity in a million. Furnace silicon is turned into a tetrahalide or silane and decomposed again; zone refining finishes it. A thin molten zone drawn along the rod carries dissolved impurities to one end, which is then cut off.

Most silicon goes elsewhere. The US Geological Survey reports ferrosilicon, silicon alloyed with iron, going mainly to steelworks and iron foundries, and silicon metal to makers of aluminium alloys and silicones. Sand, which is silica, is a principal ingredient of glass. Quartz melts at 1600 °C to a viscous liquid that usually supercools into a glass rather than crystallising.

Properties

Properties of silicon Standard atomic weights from IUPAC/CIAAW (abridged, 2024); other values from PubChem's periodic table, kelvin converted to °C.
Property	Value	Unit	Source
Atomic number	14
Standard atomic weight	28.085(1) Da	Da	IUPAC/CIAAW 2024
Melting point	1414 °C	°C	Los Alamos: 1414 °C
Boiling point	3265 °C	°C	Los Alamos: 3265 °C
Density	2.3296 g/cm³	g/cm³
Electronegativity (Pauling)	1.9
Electron configuration	1s² 2s² 2p⁶ 3s² 3p²
Phase at 25 °C	solid

The standard atomic weight of this element is an interval in nature, from 28.084 to 28.086 Da; the value shown is IUPAC's conventional abridged value.

Safety

Silicon as a lump, wafer or chip is safe to handle: of the European Chemicals Agency reports gathered on PubChem, 96.3% find that it meets no hazard criterion at all. The hazards lie with the fine amorphous powder. Japan’s classification lists it as a flammable solid, signal word Danger, and an eye irritant; the International Chemical Safety Card adds that the dust can explode when mixed with air. Anyone handling the powder should read the PubChem Laboratory Chemical Safety Summary.

Questions

Is silicon a metal?

No. Silicon is a metalloid, in between a metal and a nonmetal, and OpenStax notes that such elements are typically semiconductors. It looks like a metal, grey with a lustre, yet like the nonmetals it forms covalent crystals, and like the metals it generally forms no simple negative ion. Los Alamos calls it relatively inert: halogens and dilute alkali attack it, but most acids, hydrofluoric apart, leave it alone.

Is silicon the same as silicone?

No. Silicon is the element, a grey solid with a metallic lustre. Silicones are polymers whose bonds include silicon-oxygen, silicon-carbon, carbon-hydrogen and carbon-carbon. Los Alamos describes them as made by reacting an organic silicon chloride, dimethyl silicon chloride for one, with water, and says they range from liquids to hard, glass-like solids. They serve as lubricants and polishing agents, as electrical insulators and in medical implants.

Who discovered silicon?

Jöns Jacob Berzelius is generally given the credit: in 1824 he prepared amorphous silicon and purified it by washing the fluosilicates out repeatedly. Davy, according to Los Alamos, took silica for a compound rather than an element, and in 1811 Gay-Lussac and Thenard probably made impure amorphous silicon when they heated potassium with silicon tetrafluoride. Crystalline silicon came in 1854, from Henri Sainte-Claire Deville. The name is from silex, Latin for flint.

Why doesn't silicon form long chains and double bonds like carbon?

Carbon's chemistry rests on the strength of the carbon-carbon bond, and Los Alamos notes that silicon cannot build stable compounds from very long chains of its own atoms. Elements below the second period form pi bonds, the sideways overlap behind a double bond, less readily than carbon, and those they form are weaker. So carbon dioxide is a small molecule with two double bonds, while silicon dioxide is an endless network of single bonds.

Why is silicon's atomic weight given as an interval?

Silicon has three stable isotopes; PubChem's record puts silicon-28 at about 92 atoms in every hundred, silicon-29 under five and silicon-30 about three. The isotopes differ slightly in their properties, and natural processes sort them, so the mix and the atomic weight vary from sample to sample. IUPAC therefore states an interval; the conventional value is 28.085 Da. Diatoms prefer silicon-28 for their shells and leave surface water richer in the other two.