Silicon – The Scintillating Element Silicon

Introduction to Silicon

The element silicon (Si) is a hard, brittle, crystalline solid. It is a metalloid with a blue-gray luster. The name silicon is derived from the Latin word “silicis” meaning “flint”. Notably, the element has many uses in the modern economy. In fact, the late 20th century and 21st century have been dubbed “The Silicon Age.”

Ten Interesting and Fun Facts about Silicon

• Much of the mineral chemistry field centers around crystallization and extraction of silicates.
• Despite modern associations with computing and high-tech industries, silicon, as a key ingredient of rocks and stones, has a history of human use reaching back to the stone age.
• A popular misconception is silicon and silicone are the same substance. Although silicone includes silicon, the two substances differ greatly in their properties.
• 1954 witnessed the creation of the first commercial silicon transistor.
• The creation of semiconductors most commonly uses sand as starting material because of its high percentage of silicon.
• Behind oxygen, silicon is the second most abundant element in earth’s crust.
• Silicon dioxide is the most common compound in earth’s crust.
• Pure Si element has the same crystal organization as diamond. This is because carbon and silicon are such closely related elements.
• Clay mostly comprises of silicates.
• In 2015, the total volume of silicon-based semiconductors manufactured globally surpassed 10 million square inches.

Silicon in the Periodic Table

Silicon, atomic symbol Si, has an atomic number of 14, below carbon and to the right of aluminum. This element is in the metalloid family and has four valence electrons. Hence, it is not a very reactive element.

Silicon has an electronegativity of 1.9 (Pauling scale). Silicon’s typical electron configuration is 1s²2s²2p⁶3s²3p² . Additionally, other elements in the metalloid family include Arsenic, Germanium, Tellurium, Polonium, Boron, and Antimony. These elements share many physical and chemical properties.

The Element Silicon in our Bodies

Although present in trace amounts, extent to which the human body requires silicon in order to function remains unclear. Some scientists speculate Si helps develop collagen. Collagen, a structural protein, partially makes up the connective tissue of animals. Osteoporosis patients, as well as patients for other skin and bone-related health issues, take Si as supplement. Dietary sources of of the element include meat, milk, fruits, vegetables, and even water, depending on where it comes from.

Alloys of the Element Silicon

Si forms alloys with several metals, including but not limited to aluminum, iron, and magnesium. Although the use of silicon in electronics garners the most attention, much of Si produced actually goes into alloys used in the automobile industry.

Aluminum-Si alloys (sometimes called silumin) are a lightweight, high-strength class of alloys known for their resistance to corrosion. This makes them ideal for use in humid environments. Common uses include casting, pistons, and internal combustion engine blocks. Al-Si-Cu-Mg alloys have similar properties to silumin, but they are heat treatable.

Ferrosilicon, an alloy of silicon and iron, is obtained by reducing a mixture of iron oxide and silica with carbon. The manufacturing of acid-resistant alloys uses FeSi.

Alloys of Si belong to a family of alloys known as silicides. Examples include CaSi₂, Cu₁₅Si₄, Mg₂Si, Fe₂Si, FeSi, CoSi, Nisi, CaSi₂, and many more.

Applications in the Modern World

In Electronics

Electronics use highly purified silicon. For this use, the Si must have fewer than one in ten billion atoms of impurity. This very rare pure sample is then doped with a few parts per billion of phosphorous, boron, or other specific elements to create the base semiconductor. This base semiconductor is the basic component for transistors and microchips. This process has made the information technology revolution possible.

In Silicones

Silicon is also used to make silicones. Silicones are silicon-oxygen polymers with attached methyl groups. In oil form, silicone works well as a lubricant, thus making it a useful ingredient in hair conditioners, gels, and cosmetics. Additionally, silicone rubber functions well as a waterproof sealant. Further, its uses include to seal windows or broken pipes. Breast implants and facial implants use silicone in its solid/gelatinous form.

In Medicine

Silicon nitride is a long standing orthopedic biomaterial. Although originally developed as a ceramic material for industrial applications, its high strength and resistance to fracture under extreme operating conditions have made it an attractive material to promote bone fusion in spinal surgery. Clinical trials have now begun with regards to its potential use in prosthetic hip replacement.

The Discovery of Silicon

Si was discovered by Swedish chemist Jöns Jakob Berzelius. He successfully isolated the new element by heating potassium fluorosilicate in his lab in 1824.

Where is Si Present in the Universe?

We have already discussed how silicon is a very common element on earth. However, it is also found in space. Using spectroscopy, Japanese scientists have identified molecules that contained this element in the clouds of gas surrounding some stars. In space, specifically, silicon is often found in the form of silicates within clouds of dust. More reactive Si compounds are found in the gases of the interstellar medium.

Compounds, Reactions, Oxidation states, Isolation

Chemical Properties of the Element

Si exhibits similar chemical behaviors to metals. It is electropositive, with a bonding pattern similar to that of carbon. Si is somewhat reactive with oxygen in the air, but it is only reactive with nitrogen at very high temperatures. Elemental Si does not react with water under normal conditions.

Si Compounds

With similar bonding properties to carbon, Si can and does form compounds with elements from all over the periodic table.

Silicon Carbide (SiC)

By heating carbon and sand in an electric furnace, SiC forms. This compound has a similar structure to diamond. It serves as an abrasive, but also has use as a semiconductor.

Silicon Dioxide (SiO₂)

Also known as silica, this compound occurs in nature as quartz crystals. It has polymorphs cristobalite, and tridymite (same material, different crystal structure). Different forms of these crystals polarize light at different angles.

Silicic acid (H₄O₄Si)

A weak acid with a ligancy of four, meaning the Si atom occupies the center of four oxygen atoms. Silicic acid groups together, and forms higher-level structures with itself in the presence of water.

Sodium silicate (Na₂SiO₄ or Na₆Si₂O₇)

Also known as water glass, sodium silicate is available for commercial use and serves as a fireproofing treatment for wood and cloth.

Isolation of Silicon

Although Berzelius heated silica with potassium to purify silicon in 1824, today, industry uses other techniques. Methods differ depending on the starting source. It is separated from sand (SiO₂) using carbon and heat. Another common refinement process is the shallow trench isolation method.

Oxidation States

This metalloid can possess the oxidation states of -4, +2, and +4.

Physical Properties of Silicon

• Symbol: Si
• Melting point (Celsius): 1410
• Boiling point (Celsius): 2355
• Density (g cm^-3): 2.33
• Atomic mass (amu): 28.09
• Atomic number: 14
• Electronegativity (Pauling scale): 1.9
• Classification: Metalloid
• Crustal abundance: 27.7%
• Electron configuration: [Ne]3s²3p²
• Key isotopes: ²⁸Si, ²⁹Si, ³⁰Si, and ³²Si (not stable)
• Toxicity: Inert, non-toxic for humans

Where can I buy Elemental Silicon?

The pure element sells through chemical suppliers like Sigma Aldrich, ranging from $1-50 per gram, depending on purity, and the form it is sold in – powder, nanopowder, wafer, etc …