1. Review Intermolecular Forces

2. REVIEW
Ion-dipole
Dipole-dipole
Dipole-induced dipole

3. Which attraction does this represent?

4. Which attraction does this represent?

5. Which attraction does this represent?

6. How do Geckos Walk on Walls?
Cohesive Forces
Adhesive Forces

7. Cohesive Forces
Forces of attraction between identical molecules

8. Pull water into spherical drops
Falls as drops not a mist

9. Forces of attraction between different molecules
Adhesive Forces
Forces of attraction between different molecules
The “glue” that sticks different things together

10. Water
Holds water to surfaces

11. Liquid’s shape is determined by strength of cohesive and adhesive forces

12. If cohesive force is stronger…
Water drop will be rounder
Polar Water +
Nonpolar
Wax Surface

13. If adhesive force is stronger…
Water drop will be flatter
Polar Water +
Polar Glass
Surface

14. What is a Meniscus? curvature of a liquid's surface within a container
Cohesion and adhesion explain why this happens

15. Water is a polar molecule
Within liquid water, each molecule's partial positive charge is attracted to its neighbor's partial negative charge. This is the origin of the cohesive forces within water.

16. net downward pull
no net pull

17. How does this explain the meniscus curving up or down?

18. Concaves Up the Sides
When the adhesive force of the liquid to the wall is stronger than the cohesive force of the liquid, the liquid is more attracted to the wall than its neighbors

19. Concaves Down the Sides
When the cohesive force of the liquid is stronger than the adhesive force of the liquid to the wall, the liquid concaves down in order to reduce contact with the surface of the wall

20. A little water fun!

21. How many drops can fit on a penny?
Each person will receive a penny, an eye dropper, and a cup of water
Make a Guess!

22. Results Did you guess too high, too low, or right on?
Why is this able to happen?

23. How many pennies will fit in the full glass of water before it overflows?
Each person will guess – whoever is closest gets 4 extra credit points!

24. So how do geckos walk on walls?
Spatulae Adhesion
Dipole-induced dipole