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I read in a book that zeolites are formed by Aluminium replacing a silicon atom in Silicon dioxide. It says there is a negative charge formation. How does this happen? Thanks.

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There's no magic in this - just the beauty of science.

  • Imagine a lattice of $\ce{Si^{(+4)}O4}$ tetrahedrons ($\ce{Si}$ in the centres, $\ce{O}$ on the corners) connected through the edges corners (= the $\ce{O}$ atoms)

  • Replace some of the $\ce{Si^{(+4)}}$ with $\ce{Al^{(+3)}}$

As a result, the whole lattice becomes a huge polyanion.

The charges are balanced via cations, such as $\ce{H+}$, $\ce{Na+}$, etc. embedded in the pores of the lattice.

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    $\begingroup$ I'm not sure what the standard nomenclature is, but the first time I read $\ce{SiO4}$ lattice, I was confused because if $\ce{Si}$ is +4, how can there be four oxygens instead of 2? I guess the answer is that the tetrahedra are linked, so each oxygen atom is "shared" by two Si atoms...my point is, is there a better term than "$\ce{Si^{(+4)}O4}$ tetrahedrons" or not? Maybe it's just me... $\endgroup$ – Curt F. Mar 8 '15 at 4:34
  • $\begingroup$ @CurtF. As it is in Silicones ? $\endgroup$ – Rajesh Mar 8 '15 at 7:44
  • $\begingroup$ en.m.wikipedia.org/wiki/Silicon_dioxide#Structure something like this ? $\endgroup$ – Rajesh Mar 8 '15 at 7:46

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