Silicon
Atomic Data
| Atomic Number | 14 |
| Symbol | Si |
| Atomic Weight | 28.085 u |
| Density (STP) | 2.329 g/cm³ |
| Melting Point | 1413.85 °C (1687 K) |
| Boiling Point | 3264.85 °C (3538 K) |
| Electronegativity | 1.9 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p2 |
| Oxidation States | −4, +2, +4 |
| Phase at STP | Solid |
| Category | Metalloid |
| Period / Group | 3 / 14 |
| CAS Number | 7440-21-3 |
Electron Configuration
[Ne] 3s2 3p2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 2 | 14 |
| Total | 14 | 14 | ||
Isotopes of Silicon
Silicon has three naturally occurring stable isotopes. The most abundant is ²⁸Si, comprising 92.23% of all naturally occurring Silicon.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Silicon-28 | ²⁸Si | 14 | 14 | 92.23 | Stable |
| Silicon-29 | ²⁹Si | 14 | 15 | 4.67 | Stable |
| Silicon-30 | ³⁰Si | 14 | 16 | 3.1 | Stable |
Abundance & Occurrence
Silicon is present in Earth's crust at approximately 282000 ppm by mass and at approximately 650 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Crystalline silica dust (silicosis): Inhaling respirable crystalline silica (quartz, cristobalite) causes silicosis, an irreversible and potentially fatal fibrotic lung disease; it is classified as a Group 1 carcinogen (IARC).
- Silicon dust — general: Amorphous silicon dust is a nuisance respirator irritant at high concentrations; prolonged high-level exposure can cause irritation of airways even without the silicosis risk of crystalline forms.
- Silane gases: Silicon hydrides (silanes, SiH4) used in semiconductor manufacturing are pyrophoric — they ignite spontaneously in air — and require inert-gas handling and specialised safety systems.
- Silicon tetrachloride: SiCl4, used in chemical vapour deposition, reacts violently with water to produce HCl fumes; handle only in dry, ventilated environments with appropriate respiratory protection.
Silicon in the Real World
Real-World Uses
- Semiconductor devices — Ultrapure single-crystal silicon is the substrate for virtually all integrated circuits, CPUs, memory chips, and power electronics; controlled doping with boron and phosphorus creates the p-n junctions that underpin modern electronics.
- Solar cells — Silicon photovoltaic cells convert sunlight to electricity and account for over 90% of global solar panel production; monocrystalline and polycrystalline silicon offer different balances of efficiency and manufacturing cost.
- Silicones — Polysiloxane polymers (silicones) are used as flexible sealants, lubricants, anti-foaming agents, heat-resistant coatings, medical implants, and breast implant shells due to their chemical inertness and wide temperature stability.
- Glassmaking — Silicon dioxide (silica) is the primary component of soda-lime glass (windows, bottles), borosilicate glass, and quartz glass used in fibre-optic cables, laboratory ware, and UV-transmitting optics.
- Abrasives and ceramics — Silicon carbide (SiC) is one of the hardest industrial materials, used in grinding wheels, sandpaper, cutting tools, bulletproof vest inserts, and high-temperature structural ceramics for vehicle brake discs.
- Silica in construction — Sand and gravel (largely SiO₂) are the aggregate components of concrete, mortar, and asphalt, making silicon-containing minerals the most consumed solid raw material in construction globally.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is silicon used for?
Silicon is the semiconductor material underpinning modern electronics — used in virtually all integrated circuits, CPUs, memory chips, and solar cells. Silicon dioxide (silica) is the primary component of glass. Silicone polymers (polysiloxanes) are used in sealants, lubricants, medical implants, and cookware. Silicon carbide is an industrial abrasive and structural ceramic. Silica sand is the main aggregate in concrete construction.
Is silicon the same as silicone?
No. Silicon (Si) is a chemical element — a solid semiconductor used in computer chips and solar cells. Silicone is a polymer made of alternating silicon and oxygen atoms (polysiloxane) with organic groups attached, used in flexible sealants, medical implants, non-stick coatings, and personal care products. Silicone is manufactured from silicon, but the two are very different materials with entirely different properties.
Why is silicon used in computer chips?
Silicon is ideal for semiconductor devices because its electrical conductivity can be precisely tuned over many orders of magnitude by adding tiny amounts of dopant impurities (boron for p-type, phosphorus or arsenic for n-type). Silicon forms high-quality oxide (SiO₂) that serves as an excellent electrical insulator for transistor gates. It is also abundant, inexpensive, and can be refined to extraordinary purity (11 nines, 99.999999999%) needed for defect-free crystal growth.
Is silicon found in nature as a pure element?
No. Silicon is the second most abundant element in Earth's crust (about 28% by mass), but it occurs exclusively in combined form — mainly as silicon dioxide (SiO₂, as quartz, sand, and flint) and as silicate minerals (feldspars, micas, clays) that make up most rocks and soils. Pure elemental silicon does not occur naturally and must be produced industrially by reducing silicon dioxide with carbon (coke) in an electric arc furnace.