In which everyday products quartz (silicon dioxide) might be found?

Why is silicon dioxide not SiO4?

• I understand that silicon dioxide has a crystalline structure where one silicon atom is bonded to 4 oxygen atoms and 1 oxygen atom is bonded to 2 silicon atoms. But I cannot wrap my head around why it is called silicon dioxide and allocated the formula SiO2. Can anyone help to clearly explain why? Thanks!

• Answer:

  In the most common crystalline forms of silica, on average, all 4 of the points (or oxygen atoms) of the SiO4 structure (which is in a tetrahedron shape) are shared with other SiO4 tetrahedrons, and so even though you can see a Si04 tetrahedron in the crystal, it is not isolated but connected to other Si04 tetrahedrons by sharing oxygen atoms. The resulting relative amounts of silicon and oxygen in the crystalline structure leads to the net chemical formula: SiO2.  If you managed to tease a single SiO4 away from the crystalline structure, it would itself be an ion with a negative 4 charge.  Look up the different orthosilicate compounds, like Na4SiO4, which shows that SiO4 isolated is an ion, not a molecule.