Question

Which one of the following group represent 2-D silicate?

• A. $Si{O}_4^{4-}$
• B. $(S{i}_2{O}_5{)}_n^{2n-}$
• C. $S{i}_2{O}_7^{6-}$
• D. $(Si{O}_3{)}_n^{2n-}$

Answer 1

The correct option is B $(S{i}_2{O}_5{)}_n^{2n-}$

The general formula of 2-D sheet silicates is $(S{i}_2{O}_5{)}_n^{2n-}.$ Each $Si{O}_4^{4-}$ tetrahedron shares three oxygen atoms with others and thus by forming two-dimensional sheets. These silicates can be cleaved easily just like graphite. The layers are held together by weak van der Waal's forces.

THEORY
Silicates: Silicates are the minerals containing silicon and oxygen atom in tetrahedral $Si{O}_4^{4-}$ units, which are linked together in several patterns. Depending on the way the tetrahedral units are linked, the silicates are classified into the following types.

1. Ortho-silicates
2. Pyro-silicates
3. Cyclic Silicates
4. Chain Silicates
5. 2-D Sheet Silicates
6. 3-D Sheet Silicates

4. Chain Silicates:

• Simple chain silicates
• Double chain silicates

Simple chain:

• Two corners of each tetrahedron are shared.
• A long chain of a tetrahedron.
• General formula is $(Si{O}_3{)}_n^{2n-}$

Double chain:

• Two simple chains joined together by shared O atoms.
• Also known as amphiboles.
• General formula : $(S{i}_4{O}_{1}1{)}_n^{6n-}$

5. 2D-Sheet:

• 3 oxygen atoms of each tetrahedron are shared with adjacent SiO44– tetrahedrons. General formula is $(S{i}_2{O}_5{)}_n^{2n-}$
• 

6. 3D-Sheet:

• Involve all four O-atom in sharing with adjacent SiO44– tetrahedral units. Example: Quartz, Tridymite, Cristobalite, Feldspar, Zeolite.