3.2 Properties of Solids

What else do you need to know about Properties of Solids?

You must understand the specific behaviors of each, such as why ionic solids only conduct electricity when molten or aqueous, why covalent network solids (like diamond, graphite, SiO2, SiC) have high melting points and varying hardness, why molecular solids have low melting points and do not conduct electricity, and why metallic solids are conductive, malleable, and ductile. The effects of alloying (interstitial) on malleability and ductility are also included. Furthermore, you must recognize that in large biomolecules or polymers, noncovalent interactions dictate shape and functionality.

Can you do these?

• I can relate the vapor pressure, boiling point, and melting point of a substance to the strengths and types of intermolecular forces present.
• I can use particulate-level representations to communicate how intermolecular interactions establish macroscopic properties.
• I can explain the properties of ionic solids, such as low vapor pressure, high melting/boiling points, brittleness, and conditional electrical conductivity, based on strong interactions between ions.
• I can describe the structure and properties of covalent network solids (e.g., diamond, graphite, silicon dioxide) and explain their high melting points and rigidity based on strong covalent interactions.
• I can explain why molecular solids generally have low melting points and do not conduct electricity, based on their weak intermolecular forces and tightly held valence electrons.
• I can explain the properties of metallic solids (conductivity, malleability, ductility) and alloys based on the presence of free valence electrons and the arrangement of metal cores.
• I can describe how noncovalent interactions dictate the shape, functionality, and properties of large biomolecules or polymers.

How is Properties of Solids tested on the exam?

On the AP Exam, you are frequently asked to compare the physical properties of substances and relate them to the attractive forces between particles. A common pitfall is confusing intramolecular and intermolecular forces, or using vague terms like 'strong' and 'weak' instead of identifying the specific intermolecular force and explaining its relative strength. You must be able to determine which forces are most important in explaining differences in properties like melting points, boiling points, and vapor pressures. Questions may also require you to explain the connection between particulate-level and macroscopic properties using models and representations (Skill 4.C).