Question

Silicon exists only in the diamond structure due to the tendency to form ${{p\pi }} - {{p\pi }}$ bonds to itself.
A. True
B. False

Answer 1

To answer this question we should know what is diamond structure and the structural features of silicon such as size. Silicon is an element of the carbon family. Carbon family is known for its catenation tendency. Due to the smallest size, carbon has a high catenation tendency which decreases in the group. So, we will check the catenation tendency of silicone and factor allowing or disallowing the formation of diamond structure.

Complete step-by-step answer:
Diamond, graphite and fullerene are the allotropes of carbon. In diamond each carbon forms four bonds with four other carbon forming a perfect tetrahedron. The hybridization of each carbon is ${{s}}{{{p}}^{{3}}}$.

In graphite each carbon forms three bonds with three other carbon forming a hexagon. The fourth bond is a pi bond formed by ${{p\pi }} - {{p\pi }}$ overlapping adjacent carbon atoms. The hybridization of each carbon is ${{s}}{{{p}}^2}$. Each carbon forms three bonds in a hexagon and fourth bond with another hexagon.

The structure of other members of the carbon family depends upon the catenation tendency which in turn depends upon the size.

The size of silicon is more than carbon.so, silicon has less catenation tendency. Due to large size silicon can form diamond structure but cannot form graphite structure because large size of silicon does not allow the ${{p\pi }} - {{p\pi }}$ overlapping of adjacent carbons p-orbital.

So, silicon exists only in the diamond structure, is true but the diamond structure is not due to the ${{p\pi }} - {{p\pi }}$ bonds, it is due to the large size of silicon.

So, the sentence, silicon exists only in the diamond structure due to the tendency to form ${{p\pi }} - {{p\pi }}$ bonds to itself, is not correct.

Therefore, option (B) False, is the correct answer.

Note: When a compound can exist in two or more forms in the same physical state, all the forms are known as allotropes and this tendency is known as allotropism. The property of an atom to form a large number of covalent bonds with itself is known as catenation. Down in the group size increase and catenation decrease. As the size of an atom increases, the tendency of form ${{p\pi }} - {{p\pi }}$ bonds decreases. The structure of diamond is rigid tetrahedron. The structure of graphite is hexagonal. The graphite is conductor whereas the diamond is insulator.