Question

Are covalent crystals equivalent to a network covalent solid?

Answer 1

The short answer is `"NO"`. A covalent crystal is molecular, whereas a network covalent solid is definitely non-molecular.

Explanation:

The distinction between molecular and non-molecular substances pervades much of introductory chemistry, and the distinction helps us to understand material properties.

Network covalent solids such as diamond, or silicon dioxide, are definitely non-molecular. They consist of an infinite array of `C-C` or `Si-O-Si-O` bonds. Because there are no discrete molecules, these materials have exceptionally high melting points.

On the other hand, many organic substances crystallize from a suitable solvent to give low melting point (i.e. `50-150""^@C`) solids. These melting points are fairly low, and reflect the weaker intermolecular forces. These melting points are also characteristic, and when given an organic unknown, the best method of identification is to take the melting point, perform a few chemical tests to ascertain what type of compound you've got, and then make a few organic derivatives of the unknown, and then compare these melting points with those of the known derivatives.

You'll find several copies of this this work floating around your laboratory.