Silicon - Si
Silicon (Si) is a metalloid used in semiconductors and alloys. In water, the term “silica” usually refers to dissolved or particulate silicon dioxide species, not to elemental silicon metal.
Chemical properties · Uses and occurrence · Health effects · Environmental effects · Water and treatment
Chemical properties of silicon
| Symbol / atomic number | Si / 14 |
|---|---|
| Group / period / block | 14 / 3 / p |
| Standard atomic weight interval | [28.084, 28.086] |
| Electron configuration | [Ne] 3s2 3p2 |
| Common oxidation state | +4 |
| Density (crystalline, 20 °C) | 2.3296 g cm−3 |
| Melting point | 1414 °C |
| Boiling point | 3265 °C |
| Electronegativity (Pauling) | 1.90 |
| Non-bonded atomic radius | 0.210 nm |
| First ionisation energy | 786.5 kJ mol−1 |
| Stable isotopes | 28Si, 29Si and 30Si |
| Isolation | Jöns Jacob Berzelius, 1824 |
| CAS registry number | 7440-21-3 |
Atomic weight follows CIAAW. Intervals reflect natural isotopic variation; parentheses indicate uncertainty in the final digits. Other properties follow RSC unless noted. Atomic radii depend on their definition.
Properties, uses and occurrence
Elemental silicon is a brittle, blue-gray metalloid and an important semiconductor. It is used in electronic devices and solar cells, as well as in alloys. Silicon is also a component of glass, ceramics and cement through its compounds.
Silicon and silicone are different: silicones are polymers whose backbones contain silicon and oxygen. In nature, silicon is abundant chiefly in silica (silicon dioxide) and silicate minerals such as quartz and feldspar.
Health effects of silicon and silica
Elemental silicon is distinct from silica dust. Inhalation of respirable crystalline silica from cutting, crushing or handling certain materials can cause serious lung disease. Risk depends on particle size and exposure; dust controls and applicable occupational standards are important. “Silicon” should not be used as a blanket safety description for every silicon compound.
Silicon in the environment
Weathering releases dissolved silicon species from rocks into soil and water. Diatoms and some other organisms use dissolved silica to form mineral structures. Silicon dioxide particles and soluble silicic acid behave differently in the environment and in treatment.
Silica in process water
At typical water pH, dissolved silica is commonly present as weakly ionised silicic acid; natural waters can also contain colloidal silica and suspended silicate particles. These forms do not necessarily respond to treatment in the same way, so sampling and analysis should identify what the reported “silica” measurement represents.
Silica can limit recovery in reverse-osmosis and other concentration processes because concentrating the feed can lead to silica scale or deposits. Risk depends on dissolved silica, pH, temperature, recovery and other water chemistry. Evaluate the full water analysis and operating conditions; do not assume that a generic antiscalant or one solubility number guarantees scale control.
Clarification or filtration may address particulate forms, while dissolved silica often requires process-specific approaches. Use representative testing and monitor the concentrate and treated water. See silicon in water and the silica solubility and scaling calculator.
Silicon page last reviewed: by Lenntech.
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