• Skip to main content
  • Skip to secondary menu
  • Skip to primary sidebar

Class Notes

Free Class Notes & Study Material

  • Home
  • Class 1-5
  • Class 6
  • Class 7
  • Class 8
  • Class 9
  • Class 10
  • Class 11
  • Class 12
  • NCERT Solutions
Home » Class 11 » Chemistry » p-Block Elements » Silicates

Silicates

Last Updated on April 6, 2023 By Mrs Shilpi Nagpal

A large number of silicate minerals exist in nature. Some of the important minerals are : feldspar i.e. Albite

NaAlSi3O8, zeolites e.g. chabazite Ca2[(AlO2)4 (SiO2)8.H2O, micas [KAl2(Si3AlO10(OH)2] and asbestos [Mg3(Si2O5)(OH)4].

The basic structural unit in silicate is the SiO44- terahedra.

The two important man-made silicates are glass and cement.

Silicates are the compounds in which the anion present are either discrete SiO44-  tetrahedra or a number of such units joined together through corners.

Discrete unit

Types Of silicates

Silicates are classified into the following different types depending upon the number of corners of SiO44-  tetrahedron shared with other tetrahedra through oxygen atoms. The negative charge on silicate structure is neutralized by positively charged metal ion.

1) Orthosilicates : These are simple silicates containing discrete SiO44- tetrahedra i.e. there is no sharing of corners with the other.

For examples : Zircon (ZrSiO4) , Forestrite (Mg2SiO4) , wellimite (Zn2SiO4) , Phenacite (Be2SiO4).

structure of orthosilicate

2) Pyrosilicates : When two SiO44- tetrahedra share one corner, Si2O7 6-  anion is formed. Silicates containing this anion are called pyrosilicates. The structures possessed by them are also called island structures.

For example : Thortveitite Sc2(Si2O7) , Hemimorphite Zn3(Si2O7)Zn(OH)2·H2O

structure of pyrosilicates

3) Cyclic or ring silicates : If two oxygen atoms per tetrahedra are shred to form closed rings such that the structure with the general formula (SiO32-)n  or (SiO3)n2n- are obtained, the silicate containing these anions are called cyclic silicates.

structure of ring silicates

For example: Si3O96- , Si6O1812- , Wollastonite (Ca3Si3O9) , Beryl (Be3Al2Si6O18)

4) Chain silicates : If two oxygen atoms per tetrahedron are shred such that a linear single strand chain of the general formula (SiO32-)n or (SiO3)n2- is formed, then the silicates containing these anions are called chain silicates.

structure of chain silicates

For example:  Spodumene ( LiAl(SiO3)2) , Diopside (CaMg(SiO3)2)

If two chains are cross linked, the resulting double-stranded silicates having the formula [(Si4O11)n6-] are called amphiboles.

For ex: Tremolite ( Ca2Mg5(Si4O11)(OH)2) , asbestos (CaMg3O(Si4O11)

5) Sheet silicates: The sharing of three corners results in an infinite two dimensional sheet structure of the formula (Si2O5)n2n- or (Si2O52-)n

Silicates containing these anions are called sheet silicates.

structure of sheet silicates

6) Three dimensional silicates:  If all the four corners are shared with other tetrahedra,  three-dimensional structure network is obtained.

For example: quartz, tridymite and cristobalite

Zeolites

If some of the Silicon atoms in a three-dimensional network silicates are replaced by Al3+ ions, the overall structure thus obtained carries a negative charge and is called and aluminosilicates. Therefore to balance the negative charge ,some cations such as Na+ , K+ and Ca2+ are incorporated into structure.

Such three dimensional aluminosilicates are called feldspar (KalSi3O8) and zeolites(NaAlSi2O6·H2O).

Zeolites are widely used as a catalyst in petrochemical industries for cracking of hydrocarbons and isomerisation.

For example: ZSM-5 is used to convert alcohols directly into gasoline. Hydrated zeolites called permutit are used as ion exchangers in softening of hard water.

Share with Friends

Filed Under: Chemistry, Class 11, p-Block Elements Tagged With: amphiboles, asbestos, chain silicates, cycylic silicates, feldspar, island structure, micas, orthosilicates, pyrosilicates, sheet silicates, silicates, three-dimensional silicates, types of silicates, unit in silicates, use of ZSM-5 zeolite, zeolites

Reader Interactions

Comments

  1. Gyanu says

    July 7, 2020 at 7:14 pm

    Thank you sooo much.
    It was very helpfull……each type is explained so well.

Primary Sidebar

Recent Posts

  • NCERT Solutions for Exercise 1.5, Class 11, Mathematics
  • NCERT Solutions for Exercise 1.4, Class 11, Mathematics
  • NCERT Solutions for Exercise 1.3, Class 11, Mathematics
  • NCERT Solutions for Exercise 1.2, Class 11, Mathematics
  • NCERT Solutions for Exercise 1.1, Class 11, Mathematics
  • Facebook
  • Pinterest
  • Twitter
  • YouTube

© 2016 - 2023 · Disclaimer · Privacy Policy · About Us · Contact Us