Silicates

Silicates are an intrinsic part of the very infrastructure that we use every day and have major contributions to most industrial applications. This paper will, therefore, explore the exciting world of silicates by describing the definitions and types and their major roles in our daily lives and academic studies.

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This Story also Contains

1. Silicates
2. Silicate Types and Their Structures
3. Some Solved Examples
4. Summary

Silicates

Silicates are minerals built up from silicon and oxygen atoms, usually combined with other elements—the aluminum, iron, magnesium, and calcium groups.
These are the biggest and most important class of rock-forming minerals, constituting about 90% of the Earth's crust. The basic building block of silicates is the silicon-oxygen tetrahedron—a molecular structure in which one silicon atom is surrounded by four oxygen atoms. This tetrahedron becomes able to link with each other in various ways, forming different silicate structures. Silicates, then, based on how these tetrahedra are arranged and bonded with each other, determine their classification. Major categories include nesosilicates, inosilicates, phyllosilicates, and tectosilicates—which have their distinctive characteristic and properties—classify into four major groups.

A large number of silicate minerals exist in nature. Some examples are feldspar, zeolites, mica, and asbestos. The basic structural unit of silicates is SiO₄^4– in which the silicon atom is bonded to four oxygen atoms in a tetrahedron fashion. In silicates either the discrete unit is present or a number of such units are joined together via corners by sharing 1,2,3 or 4 oxygen atoms per silicate unit. When silicate units are linked together, they form chains, rings, sheets, or three-dimensional structures. The negative charge on the silicate structure is neutralized by positively charged metal ions. If all four corners are shared with other tetrahedral units, a three-dimensional network is formed. Two important man-made silicates are glass and cement.

Silicate Types and Their Structures

Chain silicates

Chain silicates are formed by sharing two oxygen atoms by each tetrahedral. Anions of chain silicate have two general formulas, i.e, (SiO₃)_n^2n- and (Si₄O₁₁)_n^6n-.

Two-dimensional silicates

In such silicates 3-oxygen atoms of each tetrahedral are shared with adjacent SiO₄^4- tetrahedral. Such sharing forms 2-D sheet structure as shown below.

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Some Solved Examples

Example 1
Question:
The basic structural units of feldspar, zeolites, mica, and asbestos are:
1. $\left(\mathrm{SiO}_3\right)^{2-}$
2. $\mathrm{SiO}_2$
3. $\left(\mathrm{SiO}_4\right)^{4-}$
4.

Solution:
(i) Zeolite: It is also known as hydrated aluminum silicate.

(ii) Mica: It is a potassium aluminum silicate$K A l_3 S i_3 O_{10}\left(O H_2\right)$

(iii) Asbestos: It is a hydrous magnesium silicate with a chemical composition $\mathrm{Mg}_3 \mathrm{Si}_2 \mathrm{O}_5(\mathrm{OH})_4$

(iv) Feldspar: It is a potassium silicate $\mathrm{KAlSi}_3 \mathrm{O}_8$ and there are various sub-types of Feldspar available in the Earth's crust.

(Right arrow) Silicate is a general name given to a group of minerals that have silicon-oxygen bonds with the general formula $\left(\mathrm{SiO}_4^{x-}\right)_n$

Therefore, option (3)

Example 2
Question:
The structural unit of pyrosilicates is

1)$\mathrm{SiO}_4^{2-}$

2)$\mathrm{Si}_2 \mathrm{O}_7^{2-}$

3) (correct)$\mathrm{Si}_2 \mathrm{O}_7^{6-}$

4)$\left(\mathrm{SiO}_3\right)_n^{2-}$

Solution:
As we have learned, pyrosilicates consist of two tetrahedral units that share one oxygen atom between them, containing the basic unit of$\mathrm{Si}_2 \mathrm{O}_7^{6-}$ anion.

An example is Thortveitite $\left(\mathrm{Sc}_2 \mathrm{Si}_2 \mathrm{O}_7\right)$

Hence, the answer is option (3)

Example 3
Question:
The structural formula of cyclic silicates is:
1. $\left(\mathrm{SiO}_2\right)_n$
2. $\left(\mathrm{SiO}_2\right)_n^{2 n-}$
3. $\left(\mathrm{SiO}_3\right)_n^{2 n-}$
4. $\left(\mathrm{Si}_2 \mathrm{O}_7\right)_n^{2 n-}$

Solution:
Cyclic or ring silicates contain $\left(\mathrm{SiO}_3\right)_n^{2 n-}$ ions that are formed by linking three or more tetrahedral $\mathrm{SiO}_4^{4-}$ units. Each unit shares two oxygen atoms with other units.

Hence, the answer is option (3)

Summary

From the buildings we live into the day-to-day technologies we use, silicates reside at the base.
This paper has been able to discuss, in some detail, the basic concepts of silicates, their types and structures, and the broad scope of application. Knowing about the silicates, we realize how critical materials have been to modern life and the development of technology. The silicates remain decisive in shaping our future, be it construction, electronics, or environmental management.