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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: galpinj on June 11, 2019, 08:32:06 PM

Title: Is quartz a silica atom bound to three or four oxygen atoms:
Post by: galpinj on June 11, 2019, 08:32:06 PM: Hey everyone,

I was reading about quartz and how it is a crystalline structure based off a tetrahedron (silicon in the center and 4 oxygen molecules around it). However, all the images (including those from Wikipedia and UNSW Sydney) show quartz as a silica atom attached to only three oxygen atoms. This type of image is also rampant when I do a google search, so I have to ask: "is quartz (and glass) a silica atom bound to three or four oxygen atoms"? If it is bound to four, why are they only showing three bonds in the images?

I attached a couple images for the group to see what I mean
Title: Re: Is quartz a silica atom bound to three or four oxygen atoms:
Post by: Borek on June 12, 2019, 02:56:53 AM: These are poorly drawn, flat 2D representations of a 3D structure, kind of a flattened cross section. As you wrote, Si atom sits in the center of a tetrahedron with four oxygen atoms (not molecules!) occupying all four vertices.

Sadly, it is quite difficult to represent this structure in a clear, unambiguous way on a paper.
Title: Re: Is quartz a silica atom bound to three or four oxygen atoms:
Post by: AWK on June 12, 2019, 03:04:09 AM: These are projection drawings and for the inexperienced chemist they have the value of "nice patterns". You can take a look yourself and make real drawings of quartz and thousands of other organic and inorganic compounds using Mercury and CIF files
https://www.ccdc.cam.ac.uk/support-and-resources/Downloads/
http://rruff.geo.arizona.edu/AMS/minerals/Quartz
Title: Re: Is quartz a silica atom bound to three or four oxygen atoms:
Post by: AWK on June 12, 2019, 06:06:39 AM: different projection of the same quartz. The tetrahedral arrangement of silicon can be presented
Title: Re: Is quartz a silica atom bound to three or four oxygen atoms:
Post by: galpinj on June 12, 2019, 11:12:11 AM: Wow, thank you, everyone! This completely resolves my question, and I will definitely take a look at the website that was linked.
Title: Re: Is quartz a silica atom bound to three or four oxygen atoms:
Post by: David Tan on June 14, 2019, 04:17:31 PM: Si is connected to 4 oxygen atoms if you look at its 3D structure. Tetrahedral shape with respect to the Si atoms.