Silicon is the second most abundant element within the Earth’s crust, commonly found locked within compounds like silica, which forms the basis of common materials such as sand and rock. Although widespread, its strong chemical affinity for oxygen made it particularly resistant to early isolation attempts. For chemists in the early 19th century, the challenge was finding a chemical process powerful enough to break the bond and extract the pure substance. This difficulty set the stage for the prolonged scientific effort to isolate the element that would later become foundational to modern technology.
Early Attempts to Decompose Silica
The suspicion that silica was an oxide containing a novel element began with chemists like Antoine Lavoisier in the late 18th century. Sir Humphry Davy made the most significant early efforts to prove this theory in the early 1800s. Davy, known for his work in electrochemistry, attempted to use electrolysis on silica, but he was unable to fully reduce the compound and only produced impure alloys. Believing the substance would be metallic, Davy proposed the name “silicium,” derived from the Latin word silex or silicis, meaning flint.
The first preparation of an impure form came from French chemists Joseph Louis Gay-Lussac and Louis Jacques Thénard around 1811. They achieved this by reacting potassium metal with silicon tetrafluoride at high temperatures. The resulting product was an amorphous, brownish powder, but they did not fully recognize or characterize it as a distinct new element. Their method demonstrated a chemical pathway to reduce the silicon compound, but the lack of thorough analysis meant the definitive discovery would be credited to a later scientist.
Jöns Jacob Berzelius and the 1823 Isolation
The Swedish chemist Jöns Jacob Berzelius finally achieved the definitive isolation of amorphous silicon in 1824, building upon earlier attempts. Berzelius was a meticulous analytical chemist who understood the necessity of purification to prove the existence of a new element. His key reaction involved the reduction of potassium fluorosilicate (\(\text{K}_2\text{SiF}_6\)) using molten potassium metal (\(\text{K}\)). Berzelius’s rigorous purification steps, a variation of the reaction used by Gay-Lussac and Thénard, secured his credit for the discovery.
The reaction mixture was subjected to repeated washing to remove byproducts, specifically the fluosilicates, leaving behind a relatively pure brown powder. This material was amorphous silicon, a form that lacked the organized crystalline structure common today. Berzelius followed this isolation with a thorough chemical characterization, demonstrating that the brown powder was a distinct element. This successful isolation and characterization, published in 1824, confirmed Lavoisier’s original suspicion that silica was the oxide of an undiscovered element.
Formal Classification and Early Purification Efforts
Following his isolation, Berzelius adopted Davy’s proposed name, “silicium,” and classified the new element based on its chemical properties. He recognized that the element shared characteristics with non-metals like boron and carbon, correctly placing it within the emerging framework of chemical elements. The English name was later formally changed to “silicon” by Thomas Thomson, replacing the metallic-sounding “-ium” ending with the non-metal suffix “-on” to better reflect its nature.
The amorphous brown powder Berzelius produced was the element in its reduced form, but the highly ordered crystalline form remained elusive for several more decades. The crystalline allotrope, which exhibits a metallic luster and blue-grey color, was first prepared in 1854 by the French chemist Henri Étienne Sainte-Claire Deville. Deville produced these purer, hard, octahedral crystals by passing silicon chloride vapor over molten aluminum. The creation of both the amorphous and crystalline forms confirmed the element’s distinct nature.