Unit 10 Chem- 10.2
Intermolecular Forces
- Forces of attraction BETWEEN molecules
- Not as strong as intramolecular forces (bonds)
Types of intermolecular forces 1- London Dispersion Forces
Attractive force caused by uneven distribution of electrons
-Weakest IMF
Types of intermolectular forces 2- Dipole-Dipole forces
Attractive forces between permanently polar molecules
Types of intermolecular forces 3- Hydrogen Bonding
special type of dipole-dipole force occurring between hydrogen and an electronegative element
What does hydrogen must be bonded to?
O, N, F
When does attraction occur
between molecules
Evaporation
The transition of particles from liquid to gas at a temp below the boiling point
- the escape of high energy particles from the surface of a
liquid
Criteria for Evaporation
- Must be at the surface of the liquid
- Must have enough energy to break IMF's
Vapor Pressure
the pressure exerted by gas particles above a liquid
- result of evaporation
Vapor Pressure and IMF's
The weaker the attractive forces, the higher the vapor pressure
- More volatile liquid
What is vapor presssure dependent on
temperature
Boiling
rapid phase transition from liquid to gas (vapor)
- bubbles due to vapor pressure being equal to atmospheric pressure
Evaporation
temp below boiling point
- vapor pressure is less than Atmospheric pressure
- Temp of liquid increases
- No bubbles
Boiling 2
- Vapor pressure = Atmospheric pressure
- Temp of liquid remains constant
- Bubbles form
Normal boiling point
The temp a liquid will boil at when the vapor pressure above the liquid is 1atm (760mmHg)
Higher the altitude
lower the atmospheric pressure
Lower the atmospheric pressure
lower the boiling point
Weaker intermolecular Attraction
= Higher VP = boil at lower temps