1. Intermolecular Forces & Properties

2. IMFs and Properties IMFs are Intermolecular Forces
London Dispersion Forces
Dipole interactions
Hydrogen bonding
The number and strength of the intermolecular forces affect the properties of the substance.
It takes energy to break IMFs
Energy is released when new IMFs are formed

3. IMFs and Changes in State
Some IMFs are broken to go from solid  liquid. All the rest are broken to go from liquid  gas.
Breaking IMFs requires energy.
The stronger the IMFs, the more energy is required to melt, evaporate or boil.
The stronger the IMFs are, the higher the melting and boiling point

4. Water Water is a very small molecule
Based on its size, water should be a gas under normal conditions
However, because water is polar and can form dipole interactions and hydrogen bonding, its melting point is much higher
This is very important because we need liquid water to exist!

5. IMFs and Viscosity Viscosity is the resistance to flow
Molasses is much more viscous than
water
Larger molecules and molecules with high IMFs become inter- twined and “stick” together more
The more the molecules “stick” together, the higher the viscosity

6. Solubility
In order from something to be dissolved, the solute and solvent must break the IMFs they form within itself
They must then form new IMFs with each other

7. Solubility
Solvent, water (polar) + -
- +
Solute, sugar (polar)
Water particles break some intermolecular forces with other water molecules (to allow them to spread out) and begin to form new ones with the sugar molecules.
- +
- +
- +

8. Solubility
Solvent, water (polar) + -
- +
Solute, sugar (polar)
As new IMFs are formed, the solvent “carries off” the solute—this is “dissolving”
- +

9. Solubility
If the energy needed to break old IMFs is much greater than the energy released when the new ones are formed, the process won’t occur
An exception to this is if more energy is added somehow (such as heating)

10. Oil & Water Water is polar and can hydrogen bond, Oil is non-polar.
Much more energy is required to break apart the water than is released when water and oil combine.
Water has London Dispersion, Dipole and hydrogen bonding. That takes a lot of energy to break
Water can only form London Dispersion with the oil. That doesn’t release much energy
Therefore, oil and water don’t mix!

11. Surface Tension
Surface tension is the resistance of a liquid to spread out.
This is seen with water on a freshly waxed car
The higher the IMFs in the liquid, the more the molecules “stick” together.
The more the molecules “stick” together, the less they want to spread out.
The higher the IMFs, the higher the surface tension.

12. Soap & Water Soap has a polar head with a non-polar tail
The polar portion can interact with water (polar) and the non-polar portion can interact with the dirt and grease (non-polar).
Polar head
Non-polar tail
Soap

13. Soap & Water
The soap surrounds the “dirt” and the outside of the this micelle can interact with the water.
The water now doesn’t “see” the non-polar dirt.
Dirt

14. Soap & Surface Tension
The soap disturbs the water molecules’ ability to form IMFs and “stick” together.
This means that the surface tension of water is lower when soap is added.
The lower surface tension allows the water to spread over the dirty dishes.