Intermolecular Forces

Question 1

What are Intermolecular Forces? How many are there?

Answer 1

Intermolecular Forces (IMFs) are forces that hold atoms together within a molecule

There are 4 types of IMFs, they are:

• London Dispersion Forces (weakest)
• Dipole-Dipole Forces
• Hydrogen-Bonding Forces
• Ion-Dipole Forces (strongest)

(Disperson and Dipole-Dipole forces are Van der Waals forces)

Question 2

What are London Dispersion Forces?

Answer 2

• Weakest IMF
• Van Der Waals force
• Exists in all compounds
• Only IMF present for Nonpolar Covalent molecules

Question 3

What are Dipole-Dipole forces?

Answer 3

• Second-weakest IMF
• Van der Waals force
• Exists in Polar Covalent molecules

Question 4

What are Hydrogen-Bonding forces?

Answer 4

• Second-strongest IMF
• Exists when Hydrogen is bonded to Nitrogen, Oxygen, or Flourine (H + N, O, F)

Question 5

What are Ion-Dipole forces?

Answer 5

• Strongest IMF
• Exists in mixtures of Ionic & Polar Compounds

Question 6

What are trends of IMFs related to strength?

Answer 6

As IMF strength increases:

• Melting/Boiling Point increases
• Surface Tension increases
• Viscocity increases
• Capillary Action increases

Question 7

What is Surface Tension?

Answer 7

“Skin” on surface of a liquid that allows it to resist external force

Question 8

What is Viscocity?

Answer 8

Resistance of a liquid to flow

(peanut butter has a greater viscocity than water)

Question 9

What is Capillary Action?

What is Cohesion? What is Adhesion?

Answer 9

Liquid’s ability to flow against gravity up a narrow tube

• Can only occur when a liquid’s adhesion is greater than its cohesion

• Cohesion: Attraction between molecules within a liquid
• Adhesion: Attraction between liquid and external molecules