Quick Facts
| Property | Value |
|---|---|
| Symbol | Si |
| Atomic Number | 14 |
| Atomic Mass | 28.086 u |
| Category | Metalloid |
| Period | 3 |
| Group | 14 |
| Block | p |
| Electron Configuration | [Ne] 3s² 3p² |
Physical Properties
| Property | Value |
|---|---|
| State at 20°C | Solid |
| Density | 2.33 g/cm³ |
| Melting Point | 1414°C (1687 K) |
| Boiling Point | 3265°C (3538 K) |
| Appearance | Gray crystalline solid with metallic luster |
Atomic Properties
| Property | Value |
|---|---|
| Electron Configuration | [Ne] 3s² 3p² |
| Electronegativity | 1.90 (Pauling scale) |
| First Ionization Energy | 786.5 kJ/mol |
| Atomic Radius | 117 pm |
| Covalent Radius | 111 pm |
| Van der Waals Radius | 210 pm |
History and Discovery
Discovered by: Jöns Jacob Berzelius Year of Discovery: 1824 Location: Stockholm, Sweden
Etymology
The name "silicon" comes from the Latin "silex" or "silicis" meaning "flint" or "hard stone." Thomas Thomson suggested the name in 1831, replacing Berzelius's original "silicium."
Discovery Story
Antoine Lavoisier predicted in 1787 that silica (SiO₂) was an oxide of an undiscovered element. Humphry Davy attempted to isolate it in 1808 but failed. Jöns Jacob Berzelius succeeded in 1824 by heating potassium fluorosilicate with potassium metal. He produced amorphous silicon; crystalline silicon was first prepared in 1854 by Henri Sainte-Claire Deville.
Isotopes
| Isotope | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|
| ²⁸Si | 92.23% | Stable | - |
| ²⁹Si | 4.67% | Stable | - |
| ³⁰Si | 3.10% | Stable | - |
Occurrence
Natural Abundance
Silicon is the second most abundant element in Earth's crust (about 27.7%), after oxygen. It never occurs free in nature but is found in silicates (most rocks and minerals) and silica (quartz, sand). Beach sand is primarily silicon dioxide.
Extraction and Production
- Metallurgical Grade: Carbothermic reduction of silica in electric arc furnaces
- Electronic Grade: Purification through zone refining (99.9999999% purity)
- Sources: Quartz sand, quartzite
- Global production: about 8 million tons annually
Applications and Uses
Electronics and Semiconductors
- Computer chips and microprocessors
- Integrated circuits
- Solar cells (photovoltaics)
- Transistors and diodes
Construction Materials
- Silicones (sealants, lubricants, insulation)
- Glass and ceramics
- Cement and concrete
- Bricks and tiles
Industrial Applications
- Aluminum-silicon alloys for casting
- Ferrosilicon for steel production
- Silicone rubber products
- Abrasives (silicon carbide)
Other Uses
- Fiber optic cables (silica glass)
- Optical lenses
- Silicone medical implants
Biological Role
Silicon may have a minor biological role in connective tissue formation, though it is not considered essential for humans.
In the Human Body
- About 1 gram present in adult body
- Concentrated in connective tissues, bones, skin
- May contribute to collagen formation
- No established dietary requirement
In Other Organisms
- Essential for diatoms (silica shells)
- Found in plant cell walls (rice, horsetails)
- Important for some marine organisms
Dietary Sources
Whole grains, vegetables, and beer contain silicon.
Safety and Hazards
Toxicity
Elemental silicon is non-toxic. However, inhaling fine silica dust causes silicosis, a serious lung disease.
Handling Precautions
- Crystalline silica dust is hazardous (use respiratory protection)
- Molten silicon is extremely hot and reactive
- Silicon carbide dust can irritate skin and eyes
- Standard industrial hygiene practices for dust control
Environmental Impact
Silicon mining and processing have typical industrial impacts. Silicates are naturally abundant and environmentally stable.
Interesting Facts
- Silicon Valley is named after silicon's importance in the computer industry
- Ultra-pure silicon for electronics costs about $1,000/kg, while metallurgical grade costs about $2/kg
- Silicon is the basis of most computer chips—a single microprocessor can contain billions of silicon transistors
- Glass is made primarily from silicon dioxide (silica)
- Silicon has a diamond crystal structure, similar to carbon