Lecture 20: Intermolecular Forces and Condensed Phases What causes molecules (or atoms or ions or …) to stick to each other? Potential energy curves Phase Diagrams: Single components vs. the “real” world

Van der Waals Equation of State

Predict which a cation of sodium is most strongly attracted to: Br- anion HBr molecule Kr atom H2O molecule

Predict which an atom of hydrogen is most strongly attracted to: Br- anion Na+ cation H2 molecule Kr atom H atom H2O molecule

Relative strength of interatomic/intermolecular forces: Ion – Ion (charge matters!) Open-shell atom – Open-shell atom (covalent bonds matter!) Ion – Dipole (dipoles matter!) Dipole – Dipole Special Case: Hydrogen Bond Ion – Induced dipole Dipole – Induced dipole Fluctuating dipole – induced dipole (“dispersion force”)

Which is lower in energy? (1) (2)

Potential Energy Curves

1mL of liquid water is placed into an evacuated container of volume 10mL at room temperature. What is the pressure? 10atm 1atm 0.1atm 0.01atm 0.000atm