Molecular Solid vs Network Covalent Solids

[henry3369]

Homework Statement

I'm having trouble figuring out if a solid is a molecular solid or network covalent solid.

Classify the following as a network covalent solid or a molecular solid:
1. CO2
2. SiO2

Homework Equations

Molecular solid held together by intermolecular forces
Covalent network solids are held together by covalent bonds.

The Attempt at a Solution

I know that CO2 is a molecular solid and SiO2 is a network covalent solid, but I'm not sure how I would figure that out. They both have two oxygen atoms, and carbon and silicon have the same number of valence electrons. What makes them different types of solids then?

 

[James Pelezo]

This is a topic that, honestly, can't be reduced to a few rules. It is easy to say CO₂ is this, or SiO₂ that, but to understand what you need under "The attempt at a solution" it requires a comprehensive understanding of how solid state structures are classified & how different classifications of structures interact. The statements under "Relevant Equations" above, are correct, but is only a part of the 'big picture' that you need understand in order to ID the classification of solids from formulas. I might suggest looking up 'The Solid State' in a reputable college chemistry text and spend quality time reviewing
- classification of types of solids,
- properties of solids that affect melting point, hardness & conductivity,
- crystalline structure and how it is defined, and
- structures of specific types of crystalline solids.
I wish I could say your question has a simple answer or rule, but it does not. It will be a time consuming effort to develop a good understanding, but well worth the effort. Lots of luck. :-)