Silicon is a cornerstone element in both the geological formation of our planet and the technology that defines the modern age. This element is a fundamental component of the rocks, soil, and sand that make up the Earth’s surface. In its purified form, silicon is the physical material that makes possible the digital world of computers and smartphones. Represented by the symbol Si, silicon is the second most abundant element in the Earth’s crust, found in nearly 28% of its mass, second only to oxygen.
The Element Silicon (Si)
Silicon is a metalloid, exhibiting properties of both metals and nonmetals, and holds the atomic number 14 on the periodic table. It is a tetravalent element, possessing four valence electrons that allow it to form strong bonds with other elements, particularly oxygen. Pure silicon appears as a hard, brittle crystalline solid with a distinctive blue-gray metallic luster.
The pure elemental form is extremely rare in nature because it readily reacts with oxygen. This reactivity means silicon is almost always found in compounds, accounting for its vast abundance across the planet. Its melting point is high, at 1414°C, and it is relatively inert under normal conditions, contributing to its stability in various applications.
Silicon’s Role in Earth and Nature
Silicon’s presence in the natural world is due to its strong affinity for oxygen, forming compounds like silica and silicates. Silica, or silicon dioxide (SiO2), is the most common compound, found abundantly as quartz and as the main component of common sand.
Silicates are the family of minerals that form when silicon and oxygen combine with various metals. Minerals like feldspar, mica, granite, and clay are all examples of silicates that compose over 90% of the Earth’s crust.
Beyond geology, silicon also plays a biological role in certain life forms. For instance, microscopic aquatic organisms called diatoms build their intricate external cell walls entirely from silica. Some plants, such as grasses and rice, absorb silicon from the soil and deposit it into their cell walls as silica structures. This incorporation provides mechanical strength, promoting upright growth and resistance to environmental stressors. Though not considered an essential nutrient for animals, silicon is present in trace amounts in the human body, contributing to connective tissues.
From Sand to Semiconductors
Silicon’s most celebrated application comes from its unique electrical properties, which are harnessed in the semiconductor industry. The manufacturing process begins with high-purity silica sand, which is heated with carbon in an electric arc furnace to temperatures over 2,000°C to remove the oxygen. This yields metallurgical-grade silicon, which is about 98-99% pure.
To be suitable for electronics, the purity must be increased dramatically through a complex chemical refinement process involving gaseous compounds like trichlorosilane. This process removes trace impurities, resulting in electronic-grade silicon with a purity of 99.999999% or greater.
The purified material is then melted, and a single crystal is grown using the Czochralski process, where a seed crystal is slowly pulled from the molten silicon. This single-crystal silicon is formed into large cylindrical ingots, which are then precisely sliced into thin, flat discs called wafers.
The electrical behavior of the silicon is then carefully controlled by adding trace amounts of impurities, such as boron or phosphorus, a process called doping. Doping alters the conductivity of the silicon, making it a semiconductor whose electrical properties can be switched on or off. This controlled conductivity is the mechanism behind transistors, the fundamental switches in integrated circuits and microprocessors. Because silicon wafers can host billions of these microscopic transistors, they form the backbone of nearly all modern computing and communication technology. The industry’s reliance on this element is so complete that the region where much of this technology originated is known as “Silicon Valley.”
Understanding Silicon vs. Silicone
A common point of confusion arises from the similar names of the element and a related manufactured material. Silicon is the naturally occurring element, whereas silicone is a synthetic polymer derived from silicon. Silicone is a compound built on a repeating chain of silicon and oxygen atoms, which also includes carbon and hydrogen.
Unlike the hard, crystalline element, silicone is known for its flexible, rubber-like consistency and its resistance to heat and chemicals. These properties make it useful for a wide range of applications, including medical devices, flexible molds, sealants, and kitchenware. Silicone is a manufactured product whose creation relies on the purified element silicon.