Question

Write about the covalent or network solids or crystals.

Answer 1

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Answer:


$\textbf{In covalent crystals}$, the constituent particles are atoms which are linked together by a continuous system of covalent bonds throughout the crystal.


$\textbf{In other words}$, there is a continuous network of covalent bonds forming a giant three dimensional structure. They are also called $\textbf{giant molecules}$. Covalent bonds are strong and directional in nature and therefore, atoms in these solids are held very strongly at their positions.

The important characteristics of covalent crystals are:

a) The $\textbf{covalent crystals are hard}$.

b) They have extremely $\textbf{high melting point }$and may even decompose before melting.

c) They are $\textbf{poor conductor of electricity}$ and are insulators.

d) They have high enthalpies of fusion.

The $\textbf{common examples}$ of covalent crystals are : Diamond, carborundum, quartz, boron nitride etc.


$\textbf{\underline{Example of Diamond}}$:

Diamond is a typical example of covalent crystal. It has a network structure consisting of a very large number of carbon atoms bonded to each other. Each carbon atom is s$p^{3}$ hybridised and is bonded to four other carbon atoms by the single covalent bonds. Each carbon atom lies at the centre of a regular tetrahedron and the other four carbon atoms are present at the corners of the tetrahedron.


Therefore, there is a three dimensional network of strong covalent bonds. This makes diamond an extremely $\textbf{hard crystal}$ with very high melting point ( 3843 k). Since all the valence electrons of carbon are strongly held on carbon - carbon bonds, diamond is a $\textbf{poor conductor}$ of electricity.


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Answer 2

Answer:

The characteristics of covalent network crystals are as follows :

() The constituent paricles in these solids are atoms.

(2) The atoms in these crystals are held by covalent bonds forming a rigid three dimensional networknwhich gives a giant molecule. Hence, the entire crystal is a single molecule.

3) These crystals are very hard (or hardest) and most inconmpressible.

(4) They have high melting points and boiling points.

6) Since the electrons are localised they are poor conductors of heat and electricity.

(6) Example: Quartz (SiO_2,), diamond.