1. Chapter 11 Liquids, solids, and intermolecular forces

2. Intermolecular forces
Intermolecular forces – attractive forces between particles composed of matter (atoms, ions, and molecules)
These forces dictate many properties of an atom
Melting point, boiling point, pattern in a lattice, miscibility, solubility, etc.
Driving factor for intermolecular forces is Coulomb’s law!!!!
Positive and negative charges attract!!!
Depending on the magnitude of the negative or positve charge, the intermolecular force that attracts the particles will be stronger or weaker

3. Dispersion forces
Dispersion/London forces – the result of fluctuations in the electron distribution within molecules or atoms
At the point in time when the electrons are localized on one side of the atom, the region has a partial negative charge, while the opposite side of the atom would have a partial positive charge

4. Dispersion force: Atom size
Larger atoms will have greater dispersion forces
More electrons, more space, more volume in which electrons can polarize the atom
Greater dispersion force results in higher melting points and boiling points since it take more energy (higher temperature) to separate the attracted particles

5. Dispersion forces: Molecular shape
In general, higher molar mass results in greater dispersion forces
Molecular shape must also be considered, since it will determine the surface area of interaction
C5H14

7. Dipole-dipole force
Dipole-dipole force – attractive force between polar molecules
If a molecule has a net dipole it is polar and the positive region of one molecule can attract to the negative region in another molecule

8. Dipole-dipole interactions are a stronger force than dispersion forces since the dipoles are permanent instead of temporary
Every molecule has dispersion forces, but only polar molecules have dipole-dipole forces

9. Dipole-dipole force: Dipole moment
The greater the magnitude of the positive and negative charge in the dipole, the greater the force
Increasing dipole moment = stronger dipole-dipole force

10. Dipole-dipole force: Miscibility
Miscibility – the ability to mix without separating into two states
Dipole-dipole forces are present between one polar molecule and another, so they will be miscible
Dipole-dipole forces are not present between polar molecules and nonpolar molecules
Water is a polar molecule
Oil is a non polar molecule
Water and oil are not miscible, they don’t mix

11. Hydrogen bonding
Hydrogen bonding – attractive force that occurs between the H that is bonded to a very electronegative atom (O, N, F) on one molecule and a very electronegative atom on another molecule
Since there is a large electronegativity difference, the magnitude of the dipole moment is larger, resulting in a very strong intermolecular force, larger than regular dipole-dipole forces

13. Ion-dipole force
Ion-dipole force – attractive force between ions and a polar compound
Ionic compound composed of cation and anion
Cation is attracted to negative end of dipole
Anion is attracted to positive end of dipole

14. Summary of intermolecular forces

15. Practice Identify the major interaction expected for
the following molecules
Cl2
NH3
C10H22 KI
HBr
Identify the major interaction expected between
Water and ammonia (NH3)
Formaldehyde (CH2O) and methane (CH4)