Review: 1. Which of the substances has the highest normal bp? 2. Would a 50oC sample of ethanol boil under an external pressure of 50 kPa? 3. Based on the vapor pressure curves provided, which substance would have the strongest IMF’s?

Goals for the next 3 days: Draw simple representations of different types of solids that illustrate important aspects of their structure Analyze models of different solid types in order to explain the properties of these substances.

So what is a solid? Cool any gas down enough that when they collide, they do not bounce off elastically

So what is a solid? Cool any gas down enough that when they collide, they do not bounce off elastically Continue to cool the sample …

So what is a solid? Cool any gas down enough that when they collide, they do not bounce off elastically Continue to cool the sample … Ordered and organized array of closely packed particles …

So what is a solid? Ordered and organized array of closely packed particles. Particles have vibrational motion. Most solids have a repeatable crystal structure called a lattice Since particles are close-packed, solids are incompressible

What types of substances form solids? Room temperature gases or liquids (weaker IM force substances) will solidify when cooled (KE is removed until IM forces take hold) Room temperature solids are substances that have very strong intermolecular OR intramolecular attractions.

Phase Change Energy Factors: heat + S  L (melting) S  G (subliming) Endothermic heat + L  S + heat (freezing) G  S + heat (depositing) Exothermic

Chemistry of Solids Types of Solids

Chemistry of Solids Types of Solids

Molecular Solids Composed of: Molecules attracted to one another via intermolecular forces

Molecular Solids Composed of: Molecules attracted to one another via intermolecular forces If the molecules are polar the attractive force will be … If the molecules are non-polar the attractive force will be …

Molecular Solids Composed of: Molecules attracted to one another via intermolecular forces Melting points: Generally lower MP’s than other solids Stronger IM forces will result in higher melting points

Molecular Solids Electrical conduction: A substance can conduct electricity only if it has free-flowing charged particles Molecular solids are not expected to conduct electricity in any state (solid, molten, dissolved)

Molecular Solids What about the molecular structure of solid water vs. solid methane explains the higher melting point of water? Why does neither solid conduct electricity?