Question

Name the structure of silicate in which three oxygen atoms of ${{\left[ Si{{O}_{4}} \right]}^{4-}}$ are shared:
(A) pyrosilicate
(B) sheet silicate
(C) linear chain silicate
(D) three-dimensional silicate

Answer 1

Hint: Recollect the concept of silicates. Make a note about the types of silicates present and how many oxygen atoms are shared by each of them. Find out in how many types of silicates only three oxygen atoms are shared. Compare them with the options given in the question to get the answer.

Complete step by step solution:
-Silicates are inorganic chain compounds formed by tetrahedral units${{\left[ Si{{O}_{4}} \right]}^{4-}}$.
-Silicates are of seven types,
-Orthosilicates- They are the simplest silicates consisting of discrete ${{\left[ Si{{O}_{4}} \right]}^{4-}}$ units. They are very rare and are associated with cations. For example, zircone \[ZrSi{{O}_{4}}\], phenacite \[B{{r}_{2}}Si{{O}_{4}}\]
-Pyrosilicates- They formed by joining two ${{\left[ Si{{O}_{4}} \right]}^{4-}}$ units by sharing one oxygen atom to form ${{\left[ S{{i}_{2}}{{O}_{7}} \right]}^{6-}}$. For example, thortveitite $S{{c}_{2}}S{{i}_{2}}{{O}_{7}}$
-Cyclic silicates- They formed by sharing three ${{\left[ Si{{O}_{4}} \right]}^{4-}}$ in a cyclic fashion. For example, beryl $B{{e}_{3}}A{{l}_{2}}{{(Si{{O}_{3}})}_{6}}$
-Chain silicates- They are long chain having ${{\left[ Si{{O}_{4}} \right]}^{4-}}$ units which are alternately arranged on a straight chain where each unit shares two oxygen atoms. For example, spodumene.
-Double chain silicates- Two chain silicates are arranged parallel to each other and three oxygen atoms of each silicate unit are shared. For example, asbestos.
-Sheet silicates- They are two dimensional layered silicates in which three oxygen atoms are shared by each silicate unit. For example, talc, mica.
-Three-dimensional silicates- In this type, all oxygen atoms are shared. For example, quartz, cristobalite.

-Therefore, we can conclude that the correct answer is (B) sheet silicate.

Note: Learn to differentiate between each type of silicate and make a note of how many atoms are shared by each silicate. When the silicate unit is replaced by aluminate unit $AlO_{4}^{5-}$, three dimensional silicates become three dimensional aluminates. For example, zeolite, felspar.