Chemistry · Ch 11 — The p-Block Elements
Silicon Dioxide, SiO2
Silicon Dioxide, SiO2
Silicon Dioxide,
About 95% of the earth's crust consists of silica and silicates. Silicon dioxide occurs in several interconvertible crystallographic forms — quartz, cristobalite and tridymite — which transform into one another at specific temperatures.
Structure. is a covalent, three-dimensional network solid: every silicon atom is covalently bonded, tetrahedrally, to four oxygen atoms, and every oxygen atom is in turn bonded to another silicon atom (Fig. 11.6). Every corner of every tetrahedron is shared with a neighbouring tetrahedron, so the entire crystal is effectively one giant molecule, built up of eight-membered rings of alternating Si and O atoms.
Reactivity. The Si–O bond enthalpy is very high, so ordinary silica is almost chemically inert — it resists attack by halogens, hydrogen, and most acids and metals even at high temperature. It IS attacked, however, by hydrofluoric acid and by sodium hydroxide:
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What this figure shows. A flat, grid-like structural diagram showing repeating -Si-O-Si-O-Si-O-Si- chains drawn horizontally across three stacked rows, with each silicon atom also connected by vertical lines to oxygen atoms above and below it, and those oxygens in turn connecting to further Si-O-Si chains above and below — forming an extended lattice/grid pattern of alternating Si and O atoms linked in both horizontal and vertical directions, representing the continuous three-di …