Silicon_dioxide - Wikiparency

# Silicon dioxide  ## Microsims — three.js ### Silicon dioxide (three.js) <div class="microsim-player"> <iframe src="https://wikitube-3d-microsims.netlify.app/Silicon_dioxide.html" width="100%" height="620" frameborder="0" loading="lazy" sandbox="allow-scripts allow-same-origin" title="Silicon dioxide — three.js microsim"></iframe> </div> **Open it full-screen:** [Silicon_dioxide.html](https://wikitube-3d-microsims.netlify.app/Silicon_dioxide.html) · library `threejs` · route `microsim/threejs/` ### Related microsims Live sims on neighbouring articles: - [[Allotropes_of_oxygen]] - [[Atomic_orbital]] - [[Hemoglobin]] - [[Hydrogen_bond]] - [[Molecular_orbital]] - [[Ozone_layer]] *Sim hosted off-article; the article owns the reference, not the runtime (WIKI_RULES §10.4). Placed by `g08_place_microsims.py`.*  ## Overview Oxygen is usually introduced as a gas, which understates it. By mass oxygen is roughly 46 percent of the Earth's crust -- more than every other element combined -- and almost all of it is locked into silicate minerals rather than floating in the air. Silicon dioxide is the archetype of that structural role, and quartz is one of the most abundant minerals on the planet. The formula SiO2 is a stoichiometric ratio, not a molecule. There is no discrete SiO2 unit anywhere in quartz or in glass. What exists is an extended covalent network of SiO4 tetrahedra joined at their corners, and the ratio falls out of the sharing arithmetic: each silicon is surrounded by four oxygens, and each oxygen bridges exactly two silicons, so Si : O = 1 : (4/2) = 1 : 2. ## The physics The building block is a SiO4 tetrahedron with Si-O bond lengths of about 161 pm and internal O-Si-O angles at the tetrahedral 109.5 degrees. Tetrahedra share corners, never edges or faces. The bridging Si-O-Si angle is about 144 degrees in alpha-quartz and is unusually soft -- it costs little energy to bend -- and that flexibility is exactly what allows the amorphous form to exist. The contrast between the two forms is the point of the sim: - alpha-quartz is crystalline: the same tetrahedra, arranged periodically in helices about the c axis, with long-range order and a narrow distribution of bridging angles. - fused silica, ordinary silica glass, has identical short-range order -- still corner-sharing SiO4, still four-coordinate silicon -- but the bridging angles are broadly distributed and there is no long-range periodicity at all. This is Zachariasen's continuous random network, and it is what the word "glass" actually means. Because the network is covalent throughout rather than molecular, melting requires breaking strong Si-O bonds across the whole solid, which is why silica melts near 1700 C. The comparison that makes the idea land is carbon dioxide: also a group-14 dioxide, but molecular, with only weak dispersion forces between discrete O=C=O units, and it sublimes at -78.5 C. Same stoichiometry, same column of the periodic table, a difference of roughly 1800 degrees -- entirely because one is a network and the other is not. ## Controls -> what each maps to | Control | Maps to | Range / values | Physical meaning | |---|---|---|---| | Structure | crystalline to amorphous | continuous | Randomises the Si-O-Si bridging angles while preserving corner-sharing and local coordination | | Representation | view mode | ball-and-stick / polyhedral / both | The two conventions crystallographers use for the same structure | | Network size | unit cells | small - large | How much of the network is built | | Show bridging angle arcs | -- | on / off | Draws the Si-O-Si angle whose distribution distinguishes crystal from glass | | Spin the network | -- | on / off | Rotation only; disabled under prefers-reduced-motion | ## Learning objective After playing, a learner can derive the 1:2 stoichiometry from corner-sharing tetrahedra, distinguish short-range from long-range order well enough to say what makes a glass a glass, and explain why a covalent network melts some 1800 degrees higher than a molecular solid of the same formula type. ## Limits and connections The amorphous endpoint is generated by randomising bridging angles on rigid tetrahedra and projecting back onto the corner-sharing constraint. That reproduces fused silica's short-range order and bridging-angle distribution, but it inherits alpha-quartz's ring topology, so the silicon sublattice retains more positional memory than a genuinely melt-quenched glass would. Silica has many further crystalline polymorphs -- cristobalite, tridymite, coesite, stishovite -- with different densities and silicon coordination, none of which are modelled here. ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Silicon_dioxide) : [Wikitube](https://en.wikitube.io/wiki/Silicon_dioxide) ## Previous hub tags Tree parent: [[Oxygen]]. Legacy hubs: `REACTION`. --- *Created 2026-08-05 - append-only - hand-authored to WIKI_REPOPULATION_PROTOCOL v1.0 section 5 - 0 deletions*