The document provides an overview of intermolecular forces, including dipole-dipole interactions, hydrogen bonding, and London dispersion forces, outlining their definitions and distinctions. It describes how these forces affect physical properties such as boiling points and real-life examples that illustrate their presence and significance. Additionally, practical laboratory activities and observations are included to reinforce understanding of intermolecular forces in action.

1. Good Morning
Physical Science

2. Understanding
Intermolecular Forces
Dipole-Dipole, Hydrogen Bonding,
and London Dispersion Forces

3. Learning Objectives
By the end of this lesson, you will be able to:
a. define Intermolecular Forces (IMFs);
b. differentiate between Dipole-Dipole, Hydrogen Bonding,
and London Dispersion Forces.;
c. relate IMFs to real-life examples and phenomena.;and
d. perform laboratory activities to observe IMFs in action.

4. Intermolecular Forces
•are forces of attraction between molecules,
not within them.
•They are weaker than intramolecular
forces, which are the chemical bonds
within a molecule.

5. Types of Intermolecular Forces
1. Dipole-Dipole Interactions: Between polar molecules with
positive and negative ends.
2. Hydrogen Bonding: A stronger type of Dipole-Dipole force,
involving hydrogen and highly electronegative atoms (N, O,
F).
3. London Dispersion Forces (LDF): Weak, temporary
attractions due to the movement of electrons, present in
all molecules but dominant in nonpolar ones.

6. Activity

7. Dipole-Dipole Interactions
• Occur between polar molecules that have a partial positive end and a
partial negative end.
• The oppositely charged ends attract each other, creating a dipole-
dipole interaction.
• Real-Life Example:
Water (H₂O) molecules are polar and attract each other through
Dipole-Dipole forces, which contribute to water’s relatively high boiling
point.
• Relation to Properties: Substances with strong Dipole-Dipole forces
have higher boiling points and melting points.

8. Hydrogen Bonding
• A special, stronger type of Dipole-Dipole interaction.
• Occurs when hydrogen is bonded to highly electronegative atoms such as
nitrogen (N), oxygen (O), or fluorine (F).
• The bond is stronger because the small size of hydrogen allows close
interaction.
• Real-Life Examples: Water: Hydrogen bonding causes water to form droplets
and gives it a high boiling point.
• DNA: Hydrogen bonds hold the two strands of DNA together.
• Relation to Properties:Hydrogen bonding explains water’s high surface tension
and why ice is less dense than liquid water.

9. London Dispersion Forces (LDF)
• Weak, temporary attractions caused by the random movement of
electrons.
• These forces are present in all molecules, but they are the only IMFs in
nonpolar molecules.
• Real-Life Examples:
1. Noble gases (e.g., helium, neon) exist as gases due to weak LDFs.
2. Oil spreads easily on a surface because it has only LDFs.
• Relation to Properties:
Substances with stronger London Dispersion Forces (more electrons)
have higher boiling points.

10. Importance
•IMFs affect the physical properties of
substances, such as boiling points,
melting points, and solubility

11. Activity 1: Dipole-Dipole Interaction
Observation:
Water spreads slower because of
strong Dipole-Dipole forces, while
acetone spreads faster due to weaker
polarity.

12. Hydrogen Bonding
Observation:
Water forms larger droplets due to
strong hydrogen bonds, while
alcohol forms smaller ones.

13. London Dispersion Forces
Observation:
The temporary charge on the balloon
induces weak LDFs in the paper,
causing attraction.

14. Assessment Question
Match the following examples to the correct
type of Intermolecular Force
1. Water forming droplets.
2.Oil spreading on a surface.
3. DNA strands held together.

15. Station 1
•Guide Questions:
1. Which liquid spreads faster?
2. What does this say about the strength of their
intermolecular forces?
Concept:
Water (polar) has stronger Dipole-Dipole
interactions, making it move slower than acetone.

16. Station 2
•Guide Questions:
1.Which liquid forms larger droplets? Why?
2. Why does water stick together more than alcohol?
Concept:
Water’s strong Hydrogen Bonding causes it to form
larger droplets compared to alcohol, which has weaker
intermolecular forces.

17. Station 3: London Dispersion Forces
•Guide Questions:
1. Why do the paper pieces get attracted to the balloon?
2. Are these attractions strong or weak compared to
other interactions?
Concept:
The temporary attraction of paper to the
balloon is due to London Dispersion Forces, a
weak intermolecular force.