The elements silicon (Si) and oxygen (O) are the two most abundant elements in soils of the world. The relatively small Si⁴⁺ cation does not exist as an independent cation but instead generally compounds with oxygen to form the oxyanion silicate, SiO₄^4-. The silicate structure forms by the formation of covalent bonds between silicon and oxygen, with the silicon bonding shell of electrons hybridizing to form a tetrahedral sp³ arrangement. Oxygen bonded to silicon may also form a tetrahedral bonding arrangement, permitting polymerization of silicates into larger structures.
A number of molecular visualizations modes have been used over the decades, each offering its own perspective of nature. Use the radio buttons below the molecular viewing window to switch between:

• the simplest model, stick
• the ball-and-stick model, most resembling the structure one would build from actual parts
• the spacefill model, assigning a fixed size to atoms of a given element, making molecular structure appear as the result of stacking spheres of different sizes. Here, Si neatly tucks into the interstitial space of the four O.
• the polyhedral representation of silicate indicates that the four O’s form the vertices of a tetrahedron (4-sided polyhedron), with Si in the center. This is a common method of representing silicates because the level of abstraction removes the distraction of the many component balls and instead allows consideration of how the silica tetrahedra are arranged.

Next: More about silicate bonding