1. Recall from Ionic Bonding…
The partially positive hydrogens of the water molecules attract and pull away the negative chloride ions.
The partially negative oxygens of the water molecules attract and pull away the positive sodium ions.
Big Question: For one substance to dissolve another, what is required of both substances?

2. Intermolecular Forces
forces between molecules

3. Intermolecular Forces
forces between molecules
Intermolecular forces are attractions between molecules.
Intermolecular forces are weaker than covalent or ionic bonds.

4. Intermolecular Forces
Are caused by molecule polarity

5. Intermolecular Forces
Determine whether a molecule is a gas, liquid, or solid at a given temperature.
Think and Share
How do you think intermolecular forces may determine the state of matter of a substance?

6. Why don’t oil and water mix?
Oil is nonpolar.
Water is polar.

7. IMF’s and Solubility
Determine the ability of substances to dissolve one another.
“Like dissolves like”
Polar molecules dissolve polar molecules and ionic compounds
Nonpolar molecules dissolve nonpolar molecules only

8. How do intermolecular forces influence the other physical properties of substances?
The diversity of physical properties among covalent compounds is mainly because of widely varying intermolecular attractions.

9. Properties of Substances
Viscosity
The ability of a substance to resist flowing

10. Properties of Substances
Surface Tension How difficult it is to break the surface of a liquid

11. Properties of Substances
Evaporation and Vapor Pressure A change from liquid to gas

12. Properties of Substances
Melting Point
The temperature at which a substance changes from solid to liquid or vice-versa
Boiling Point
The temperature at which a substance changes from liquid to gas or vice-versa

13. 3 Types of Intermolecular Forces
Listed in order of increasing strength:
London dispersion forces [low strength[
Dipole-dipole interactions
Hydrogen bonding [highest strength]
van der Waals forces=
London dispersion forces + dipole-dipole interactions
Dipole=
separation of + and – charge
a molecule with a + end and a - end

14. London Dispersion Forces
Occur in ALL molecules (non-polar and polar)
The weakest of molecular interactions
Caused by the motion of electrons
Electrons are in constant motion. At times, more electrons can temporarily be on one side of a molecule than another.
What do you think happens to the molecule when more electrons are on one side than another?

15. London Dispersion Forces
Temporary dipoles caused by the movement of electrons in a molecule.

16. London Dispersion Forces

17. London Dispersion Forces
A single dispersion force is very weak by itself.
However, when millions and millions of dispersion forces happen in a substance the force dispersion force is a significant intermolecular force.
The strength of dispersion forces increases as the number of electrons in a molecule increases.

18. At ordinary room temperature and pressure: Fluorine and Chlorine = gases Bromine = liquid Iodine = solid
Why do you think this is? Explain in terms of dispersion forces.

19. London Dispersion Forces
Occur in ALL molecules- polar and nonpolar
The only type of intermolecular force found in nonpolar molecules

20. Dipole-Dipole Forces
The + and – ends of polar molecules attract one another.
Dipole-dipole interactions are similar to but much weaker than ionic bonds.

21. Do you think Dipole-Dipole Forces will occur in nonpolar molecules?
The slightly negative region of a polar molecule is weakly attracted to the slightly positive region of another polar molecule.
Do you think Dipole-Dipole Forces will occur in nonpolar molecules?

22. Hydrogen Bonding Strongest type of intermolecular force
A specialized type of dipole-dipole force
Strongest type of intermolecular force
Hydrogen bonding always involves hydrogen
Hydrogen is bonded to a very electronegative atom.
Hydrogen bonding occurs ONLY when a H is
bonded directly to oxygen, nitrogen, or fluorine

23. Hydrogen Bonding
A single hydrogen bond has about 5 percent of the strength of the average covalent bond.
However, lots of hydrogen bonds add up to be of significant strength.
Hydrogen bonds are extremely important in determining the properties of water and biological molecules.

24. The “Glue” Between Molecules
Dispersion force
Dipole-dipole force
Hydrogen bonding
weakest
IM force
Copy this slide on the back of Do Now
strongest
IM force

25. Questions (Think-Pair-Share)
What causes dispersion forces? Which types of molecules have dispersion forces? (nonpolar or polar) What types of molecules have dipole-dipole forces?

26. Determine the strongest type of IM Force in:
Dihydrogen sulfide Sulfur monoxide Dinitrogen dihydride Carbon tetrachloride

27. How Do you Think IM Forces Affect the Following?
Viscosity
The ability of a substance to resist flowing
Surface Tension
How difficult it is to break the surface of a liquid
Evaporation
A change from liquid to gas
Sate of Matter
Boiling Point
Melting Point

28. How Do you Think IM Forces Affect the Following?
Viscosity high viscosity = STRONG IM Forces Surface Tension high surface tension = STRONG IM Forces Evaporation fast evaporation rates = WEAK IM Forces State of Matter High BP = STRONG IM Forces High MP = SRONG IM Forces