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Which of the following anions is present in the chain structure of silicates?
A
$(Si_2O_5^{2-})_n$
B
$(SiO_3^{2-})_n$
C
$SiO_4^{4-}$
D
$Si_2O_7^{6-}$
Detailed Solution
The basic unit of all silicates is the $SiO_4^{4-}$ tetrahedron; different silicates arise from the number of oxygen atoms shared between tetrahedra.
In chain silicates (pyroxenes), two oxygen atoms per $SiO_4$ tetrahedron are shared, giving polymeric anion chains of formula $(SiO_3^{2-})_n$.
Examples: spodumene $LiAl(SiO_3)_2$ and diopside $CaMg(SiO_3)_2$.
$SiO_4^{4-}$ is the discrete anion of orthosilicates (no oxygen shared).
$Si_2O_7^{6-}$ is the anion of pyrosilicates (one oxygen shared between two tetrahedra).
$(Si_2O_5^{2-})_n$ is the anion of sheet silicates (three oxygen atoms shared per tetrahedron).
So the anion present in the chain structure is $(SiO_3^{2-})_n$.
In chain silicates (pyroxenes), two oxygen atoms per $SiO_4$ tetrahedron are shared, giving polymeric anion chains of formula $(SiO_3^{2-})_n$.
Examples: spodumene $LiAl(SiO_3)_2$ and diopside $CaMg(SiO_3)_2$.
$SiO_4^{4-}$ is the discrete anion of orthosilicates (no oxygen shared).
$Si_2O_7^{6-}$ is the anion of pyrosilicates (one oxygen shared between two tetrahedra).
$(Si_2O_5^{2-})_n$ is the anion of sheet silicates (three oxygen atoms shared per tetrahedron).
So the anion present in the chain structure is $(SiO_3^{2-})_n$.