Many properties of liquids and solids are set by the strength and type of the forces holding the particles together. Because intermolecular interactions are completely overcome when a substance vaporizes, vapor pressure and boiling point are directly related to interaction strength. Melting also correlates with interaction strength, but the relationship is subtler: melting only rearranges the interactions rather than eliminating them.

The CED asks you to identify four solid types and reason from structure to property:

Ionic solids: strong ion–ion attractions give low vapor pressure and high melting and boiling points. They are brittle because displacing one layer aligns like charges. They conduct only when the ions are mobile — molten or dissolved.

Covalent network solids: atoms covalently bonded into a 3-D network (diamond) or into layers of 2-D networks (graphite). Formed only from nonmetals and metalloids, either elemental (diamond, graphite) or binary (SiO₂, SiC). Melting requires breaking covalent bonds, so melting points are very high. 3-D networks are rigid and hard because the bond angles are fixed. Graphite is soft because adjacent layers slide past one another easily.

Molecular solids: discrete covalently bonded molecules held to each other by relatively weak IMFs. Low melting points; they do not conduct because valence electrons are locked into covalent bonds and lone pairs. Polymers and very large molecules also fall here.

Metallic solids: good electrical and thermal conductors thanks to free valence electrons, and malleable and ductile because the metal cores rearrange easily. In an interstitial alloy the interstitial atoms make the lattice more rigid, decreasing malleability and ductility — but alloys keep a mobile electron sea and stay conducting.

EK 3.2.A.7 closes with biomolecules and polymers: noncovalent interactions between different molecules or different regions of one molecule dictate the shape, and the shape dictates the function.