1. Forces of Attraction Intermolecular Forces

2. Bonding Forces
Forces of attraction that hold atoms together in one structure are intramolecular (inside) forces.
metallic (mobile electrons in a solid)
covalent (nonmetals sharing electrons)
ionic (separate ions in crystal lattice)

3. Forces Between Particles
Forces that exist outside a molecule are called intermolecular forces.
(+) to (-)
attraction
Intramolecular Forces are stronger than intermolecular forces and require more energy to break.
Intermolecular attractions cause the molecules to align themselves (+) to (-).

4. Types of IMFs
Different kinds of particles have different types and strengths of attractions. F2
(nonpolar) F2
(nonpolar)
London Dispersion Force

5. Types of IMFs
Attractions between polar molecules are stronger than those between nonpolar molecules. CO
(polar) CO
(polar)
Dipole-Dipole Force

6. Types of IMFs
The strongest attraction between covalent molecules is the hydrogen bond, which occurs between H and N, O, or F only.
Hydrogen Bond
H2O
(very polar)
H2O
(very polar)
False

7. Types of IMFs
Charged particles (ions) interact with polar molecules to form an even stronger bond.
H2O
H2O
Na1+
(ion)
embed video of electric field response
H2O
Ion-Dipole Force

8. Comparison of Forces strength of attraction Are ions present?
Are polar molecules present?
Ionic Bonds
Ion-Dipole Forces
Are H atoms bound to N, O, or F?
Hydrogen Bonds
Dipole-Dipole Forces
Dispersion Forces Only no
yes
yes no no
yes
yes no
True
strength of attraction

9. IMF Observations
Intermolecular attractions explain why some substances are solids and others are liquids or gases at the same temperatures.
At 300K:
NaCl is solid
H2O is liquid
Cl2 is gas

10. IMF Observations
Ions dissolve in water due to the strength of ion-dipole forces pulling apart the ions from the crystal lattice.
False

11. Intermolecular Force Practice
1) ___________ are always stronger and require more energy to break than ____________.
dipole-dipole, ion-dipole
intermolecular, intramolecular
hydrogen bonds, dispersion forces
ion-dipole, ionic bonds
C) HB, LDF

12. Intermolecular Force Practice
2) True or False: London Dispersion Forces result from temporary shifts in the electron density of a nonpolar molecule.
True

13. Intermolecular Force Practice
3) Van der Waals Forces are forces of attraction between covalent molecules. They are divided into:
dispersion forces, dipole-dipole forces, and ion-dipole forces
dipole-dipole forces, hydrogen bonds, and dispersion forces
ionic bonds and hydrogen bonds
ion-dipole forces and ionic bonds
B) d-d, HB, LDF

14. Intermolecular Force Practice
4) True or False: Hydrogen bonds are intramolecular (bonding) forces.
False

15. Intermolecular Force Practice
5) A pair of the molecule shown below would likely exhibit which IMF most strongly?
London dispersion forces
dipole-dipole forces
ion-dipole forces
hydrogen bonds O F
B) dp-dp

16. Intermolecular Force Practice
6) A pair of the molecule shown below would likely exhibit which IMF most strongly?
London dispersion forces
dipole-dipole forces
ion-dipole forces
hydrogen bonds H H
A) LDF

17. Intermolecular Force Practice
7) A pair of the molecule shown below would likely exhibit which IMF most strongly? H N
London dispersion forces
dipole-dipole forces
ion-dipole forces
hydrogen bonds
D) HB

18. Intermolecular Force Practice
8) When heat is added to solid water, it is observed that the molecules begin to liquefy. What is happening to the molecules?
The molecules to give off heat and take up more space as they overcome hydrogen bonds.
The molecules move faster and are able to overcome the intermolecular forces.
B) move faster, breaking IMFs

19. Intermolecular Force Practice
9) Ionic solids typically dissolve into water. This is best explained by:
Multiple ion-dipole interactions overcome the force of attraction between ions.
Hydrogen bonds between ions and water are weaker than ionic bonds.
London dispersion forces overcome the ionic bonds to dissolve the crystal lattice.
A) ion-dipole overcoming ionic bonds

20. Intermolecular Force Practice
10) Methane (CH4) is a gas at room temperature. Explain using IMFs.
Since methane has hydrogen bonds, the attractions aren’t strong enough to hold the molecules together.
Since methane has polar bonds, the dipole-dipole forces are too weak to hold molecules closely together.
Since methane is nonpolar, the only interactions between molecules are very weak.
C) nonpolar