Covalent network solids typically have melting points and boiling points. the chemical formula of a network solid indicates in the molecule.

Covalent network solids typically have high melting points and boiling points.

The chemical formula of a network solid indicates in the molecule by a a formula unit.

Covalent-network solid is a chemical compound (or element) in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material.  

For example, SiO₂ is a covalent-network solid.

Silicon Dioxide has a high melting point, around 1700°C.

Silicon(IV) oxide has continuous three-dimensional network of SiO₂ units.

Both high and the ratio number of atoms

Explanation:

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.

personal, she chose to do it.