Day 8: Modeling Interparticle Interactions and Extended Structures

From Particles to Molecules: Bringing Back What You Know

Before we dive into new kinds of materials, let’s revisit a key idea from earlier in the course. Previously, we explored how neutral atoms like helium and neon can attract one another through fleeting shifts in their electron clouds: London dispersion forces (LDFs). These interactions are not bonds in the traditional sense, but they’re strong enough to explain why xenon can condense into a liquid (boiling point: –108 °C) while helium, with its low polarizability, remains a gas until just above absolute zero (boiling point: –269 °C ).

Now, we apply those same principles to molecules. Larger molecules have more electrons, more surface area for interactions with other molecules, and greater polarizability, all of which leads to stronger LDFs. That’s why nonane (C₉H₂₀) has a boiling point of 151 °C, while pentane (C₅H₁₂) boils at just 36 °C.

Keep this in mind as we move from hydrocarbons to more complex molecular and extended structures like graphite, diamond, and carbon nanotubes. The type and scale of bonding, from transient attractions like LDFs to extended covalent bonding frameworks, explains why some carbon materials are greasy, others are hard as rock, and some can carry electrical current like metal wires.

Here are links to all sections of the work for Day Eight. Be sure to complete them before your whole-class meeting.

D8.1 LDFs and Molecular Behavior

D8.2 Molecular Substances vs. Extended Solids

Day Eight Podia Problem