1. Intermolecular Forces
Unit 9 Lesson 1

2. Forces that occur BETWEEN molecules (covalent compounds)
Intramolecular (ionic and covalent) bonds are inside a compound. They are stronger than intermolecular forces.

3. * temporary - forms when electrons momentarily shift to one
When there is a positive (δ+) and a negative (δ-) side to an atom or molecule
Dipole -
Can be……
* temporary - forms when electrons momentarily shift to one
side of an atom at random
* induced - occurs when a neighboring molecule moves past
one with a temporary dipole
* permanent - the result of a polar bond in the molecular
structure

4. There are three types of Intermolecular Forces (IMFs)
1. London dispersion
Weakest of the IMFs
The only IMF found between nonpolar molecules

5. While the electrons in the 1s orbital of helium normally repel each other (and, therefore, tend to stay far away from each other), they do occasionally wind up on the same side of the atom.
At that instant, then, the helium atom has a temporary dipole (polar), with an excess of electrons on the left side and a shortage on the right side.

6. Another helium nearby, then, would have a dipole induced in it, as the electrons on the left side of helium atom 2 repel the electrons in the cloud on helium atom 1.
London dispersion forces are attractions between an induced dipole and an induced dipole.

7. 2. Dipole – Dipole Interactions
Stronger than dispersion forces
Occur between molecules with permanent dipoles (polar molecules)

8. 3. Hydrogen Bonds Strongest of the IMFs
Very strong dipole-dipole interactions that occur when hydrogen attached to N, O, or F in one molecule is attracted to a N, O, or F in another molecule
This is because of the very high electronegativities of N, O & F
* Although Cl also has a high electronegativity, it’s larger size keeps it from forming H bonds.

9. Label the molecules and the location of the H bond in between the molecules.
Hydrogen Bonds

10. Hydrogen bonds are what make water have so many special properties

11. Intermolecular Forces Affect Many Physical Properties
Viscosity – resistance of liquid to flow
Increases with stronger intermolecular forces and decreases with higher temperature.
Surface Tension - results from the inward force experienced by the molecules on the surface of a liquid
Melting & Boiling Points – stronger IMFs equal higher melting &
boiling points

12. States of Matter

13. The fundamental difference between states of matter is the distance between particles.

14. Solid Strong cohesive forces Particles in fixed lattice positions
Constant shape
Constant volume
Minimal compressibility

15. Liquid Particles are close together Not held in fixed positions
Take the shape of container
Have fixed volume
Little compressibility

16. Gas Particles are far apart Completely fill container
Easily compressed

17. The state a substance is in at a particular temperature and pressure depends on two things:
The kinetic energy (KE) of the particles
2. The strength of the attractions between the particles (IMFs)
The intermolecular forces between particles become stronger as particles are packed closer together and move less rapidly (less KE)

18. Phase Changes Melting Vaporization (boiling) Sublimation Freezing
Require Energy
Release Energy
Melting
Vaporization (boiling)
Sublimation
Freezing
Condensing
Deposition
Remember: All phase changes are physical changes!

19. Phase Diagrams
display the state of a substance at various pressures and temperatures and the places where equilibria exist between phases

20. The AB line is the liquid-vapor interface.
It starts at the triple point (A), the point at which all three states are in equilibrium.
It ends at the critical point (B); above this critical temperature and critical pressure the liquid and vapor are indistinguishable from each other.
Each point along this line is the boiling point of the substance at that pressure.

21. The AD line is the interface between liquid and solid.
The melting point at each pressure can be found along this line.

22. Below A the substance cannot exist in the liquid state.
Along the AC line the solid and gas phases are in equilibrium; the sublimation point at each pressure is along this line.

23. Phase Diagram of H2O
Note the high critical temperature and critical pressure:
These are due to the strong hydrogen bonds between water molecules.

24. Phase Diagram of Iodine
Phase Diagram of CO2
Phase Diagram of Iodine
Carbon dioxide cannot exist in the liquid state at pressures below 5.11 atm;
CO2 is a gas at normal pressures.