Chapter 11: Intermolecular Forces

Intermolecular Forces Intermolecular forces are attractions (and repulsions) between molecules.

Intermolecular Forces The extent and nature of intermolecular forces cause the three phases of matter: Solid Close particle distances “Fixed” particle positions Most ordered arrangement of particles Liquid Increased disorder in particle arrangement Particles move throughout the bulk Particles are relatively close together Gas No order in particle arrangement Particles move throughout entire container Particles are far apart

Intermolecular Forces There are four major types of intermolecular forces:

Intermolecular Forces There are four major types of intermolecular forces: 1)Ion-Ion and Ion-dipole interactions: only present when ions are present 2)Dipole-dipole interactions: only present for polar molecules

Intermolecular Forces There are four major types of intermolecular forces: 1)Ion-Ion and Ion-dipole interactions: only present when ions are present 2)Dipole-dipole interactions: only present for polar molecules 3)‘London’ Dispersion forces (Van der Waals forces): present for all molecules, increasingly important for non-polar molecules

Dispersion Forces

Dispersion Forces and Polarization Dispersion forces will increase with: Increasing polarizability Increasing surface area (“size”)

Intermolecular Forces There are four major types of intermolecular forces: 1)Ion-Ion and Ion-dipole interactions: only present when ions are present 2)Dipole-dipole interactions: only present for polar molecules 3)(London) Dispersion forces/Van der Waals forces: present for all molecules, most important for non-polar molecules 4)Hydrogen-bonding: extremely important for compounds containing H-O, H-N, H-F bonds

Hydrogen Bonding

Hydrogen Bonding In Ice

Intermolecular Forces - A Recap As intermolecular forces increase, molecules will “stick” together more (it requires more energy for molecule separation)

Boiling Point

Melting & Boiling Points

Changes in States of Matter Any change of state will cause an enthalpy change :

Changes in States of Matter

Phase Diagrams

Phase Diagram for CO 2 and Water

Vapor Pressure At the surface of all liquids, molecules are undergoing liquid-gas phase transitions. The amount of vaporization above a liquid (measured as pressure) is the vapor pressure

Vapor Pressure Curves A substance boils when its vapor pressure equals atmospheric pressure (The “normal” boiling point is for an external pressure of 1 atm)

(e) (d) (c) (b) (a) Vapor Pressure Curves The Clausius-Clapeyron Equation