Question

Which of the following is present in the chain structure of the silicates?
A) ${{\left( \text{S}{{\text{i}}_{\text{2}}}{{\text{O}}_{\text{5}}}^{\text{2-}} \right)}_{\text{n}}}$
B) ${{\left( \text{Si}{{\text{O}}_{\text{3}}}^{\text{2-}} \right)}_{\text{n}}}$
C) ${{\left( \text{Si}{{\text{O}}_{\text{4}}} \right)}^{\text{4-}}}$
D) $\text{S}{{\text{i}}_{\text{2}}}{{\text{O}}_{\text{7}}}^{\text{6-}}$

Answer 1

Hint:
Silicates are minerals containing silicon and oxygen in which the silicon and oxygen are linked to each other through tetrahedral bonds.

Complete step by step solution:
The chain structure of silicates contain silicon and oxygen bonded to each other in tetrahedral structures by sharing two oxygen atoms through ${{\left( \text{Si}{{\text{O}}_{\text{3}}} \right)}_{\text{n}}}^{\text{2n-}}$ and ${{\left( \text{S}{{\text{i}}_{\text{4}}}{{\text{O}}_{\text{11}}} \right)}_{\text{n}}}^{\text{6n-}}$ units.

Hence the correct answer is option B, each silicon atom is bonded to three oxygen atoms and this continues in a three dimensional structure to form the silicate chain structure.

Note:
There are different types of silicates: ortho, pyro, cyclic, chain, double chain, sheet or phyllosilicate, three dimensional or tectosilicates. In the orthosilicates or the nesosilicates there are simple tetrahedral units of ${{\left( \text{Si}{{\text{O}}_{\text{4}}} \right)}^{\text{4-}}}$. The orthosilicate is the strong conjugate base of the weak silicic acid. The second variety is the pyro or the soro silicate or disilicate which contains the $\text{S}{{\text{i}}_{\text{2}}}{{\text{O}}_{\text{7}}}^{\text{6-}}$ ions formed by joining two ${{\left( \text{Si}{{\text{O}}_{\text{4}}} \right)}^{\text{4-}}}$ units sharing one oxygen at a corner. Next comes the cyclic silicates which are formed by linking three or more tetrahedral units cyclically, each unit sharing two oxygen atoms. The chain silicates also known as the pyroxenes contain the ${{\left( \text{Si}{{\text{O}}_{\text{3}}} \right)}_{\text{n}}}^{\text{2n-}}$ ions formed by linking n numbers of tetrahedral units of ${{\left( \text{Si}{{\text{O}}_{\text{4}}} \right)}^{\text{4-}}}$ in a linear manner, each unit shares two oxygen atoms with the other two units. The amphiboles or the double chain silicates also share two oxygen atoms and lastly the phyllosilicates. Both the amphiboles and the phyllosilicates have three dimensional chain-like structures.