1. Chapter 14 – Liquids and Solids
14.1 Intermolecular Forces
Pgs

2. Objectives Review the difference between polar and nonpolar molecules
Identify the difference between intermolecular forces and intramolecular forces
Distinguish between the three main types of intermolecular forces

3. Let’s Review!!
Draw the Lewis Dot structure for the following molecules:
Cl2 HCl H2O

4. Intermolecular Forces
Most substances made of small molecules are gases at normal temperatures and pressures (25oC, 1atm)
Oxygen gas (O2), nitrogen gas (N2), methane gas (CH4) and carbon dioxide (CO2)
What about water (H2O)?
Intermolecular forces hold water molecules together to keep it a liquid!
Intermolecular forces are the “forces” that occur between molecules

5. Difference between Intermolecular Forces and Intramoleulcar Forces
INTRAmolecular forces occur WITHIN a molecule
Covalent and Ionic Bonds
INTERmolecular forces occur BETWEEN molecules
3 Types:
Dipole – dipole attraction
Hydrogen bonding
London dispersion forces

6. Intramolecular Forces
Low
Strength of Intramolecular forces
High
Explain that we are going to make the nonpolar to polar separation separated again and more precise
Today we are only talking about intermolecular forces for molecular compounds (Which have a smaller intermolecular force of attraction than ionic compounds)
Add polar covalent and nonpolar covalent to this and then highlight the covalent region to show that we will be defining this area more! (To add intermolecular forces and how that relates to melpting point)

7. Dipole-Dipole Intermolecular Attraction
= Intermolecular attraction between polar molecules
F Cl
dipole-dipole attractions are about 1% the strength of a covalent bond.
When the neg end of a polar molecule is attracted to the pos. end of another rmolecule
F Cl

8. Dipole-Dipole Intermolecular Attraction
= Intermolecular attraction between polar molecules
F Cl
dipole-dipole attractions are about 1% the strength of a covalent bond.
F Cl
F Cl

9. Dipole-Dipole Intermolecular Attraction
= Intermolecular attraction between polar molecules
F Cl
dipole-dipole attractions are about 1% the strength of a covalent bond.
F Cl
F Cl
F Cl
F Cl
F Cl

10. Dipole – Dipole Attraction
Dipole-dipole attractions exist between polar molecules
The positive and negative ends of the molecule are attracted to each other
In liquids, the dipoles find the best orientation to maximize the attractions and minimize the repulsions
Only 1% as strong as covalent or ionic bonds
They become weaker as the distance between the dipoles increases
In gases, the molecules are so far apart the dipole attractions are basically non-existent

11. Hydrogen Bonding Hydrogen bonds: EXTREMELY strong dipole attractions
Occur when hydrogen is bonded to F, O, or N

12. London Dispersion Forces
London Dispersion Forces:“attractions” that are found between nonpolar molecules
We know these forces exist because noble gases are liquids and solids at low temperatures!

13. London Dispersion Forces
Occur when the electrons around a nonpolar atom arrange themselves in a way to create a temporary dipole

14. London Dispersion Forces
Once the dipole is formed, it can induce other surrounding atoms to form dipoles as well
As the size of the atoms increases, the London Dispersion Forces become more significant
The motion of the atoms must be greatly slowed in order to create solids