Other Solids

Learning Goals

You will learn about three additional categories of solids: molecular solids, network solids, and amorphous solids.

Synopsis

Molecular solids are solids of covalently bonded molecules. These molecules will align themselves in the solid form to most efficiently utilize the available space. However, the arrangements will depend upon the shapes of the molecules and the types of intermolecular forces involved. We then cannot generalize as we could in the previous section.

Network solids are an array of atoms that are all covalently bonded into a massive interconnected structure such as graphite and diamond. The silicates are a networked arrangement of tetrahedral silicon atoms covalently bonded to oxygen atoms. Networked solids are generally very hard, rigid, and characterized by very high melting and boiling points. Silicon is just below carbon in the periodic table, but comparing the physical properties of SiO2 and CO2 illustrates the tremendous stability of the networked solids.

Amorphous solids do not have long-range order, as do the other solid categories we have studied. The intermolecular forces are strong enough to maintain a solid structure, but we can't determine a unit cell for such compounds. Glass is an amorphous solid and its physical properties are characteristic of such solids; for example, there is no definitive melting point as there is with other solids.

Review Questions

1.) Sketch how you think CH₄ might form a solid structure.

2.) Sketch how you think CO₂ might form a solid structure.

3.) Comment on the differences in the solid structures for CH₄ and CO₂ on the WebCT bulletin board.

4.) Try to sketch the solid structure for SiO₂ and comment on difference with CO₂.