The document discusses intermolecular forces of attraction between molecules. It describes three main types of intermolecular forces: London forces, permanent dipoles, and hydrogen bonds. London forces are the weakest and result from instantaneous dipoles formed from electron motion. Permanent dipoles form from molecules with permanent charge separation. Hydrogen bonds are the strongest intermolecular forces and require a hydrogen atom bonded to a nitrogen, oxygen or fluorine. The type of intermolecular forces present influences the phase and properties of substances.
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Intermolecular Forces of Attraction
1. What are Intermolecular Forces of
Attraction?
• We’ve discussed ionic and covalent bonds
• involve attractions between atoms
• involve the exchange or sharing of electrons
between two or more atoms
• The resulting molecules have different forces of
attraction for one another
• These are intermolecular forces
2. Why are Intermolecular Forces
Important?
• They often determine the phase a
substance is more likely to be.
• Solid, liquid, or gas
• Life science applications: DNA
3. Types of Intermolecular Forces of
Attraction
• London (or van der Waals) Forces
• Permanent Dipoles
• Hydrogen Bonds
4. London Forces
• Weakest force
• Instantaneous Dipole
• Electrons in constant
motion
• No permanent positive/
negative region
• Strength of force depends
on total # of electrons
5. London Forces
• Weakest force
• Instantaneous Dipole
• Electrons in constant
motion
• No permanent positive/
negative region
• Strength of force depends
on total # of electrons
6. London Forces
• Weakest force
• Instantaneous Dipole
• Electrons in constant
motion
• No permanent positive/
negative region
• Strength of force depends
on total # of electrons
7. London Forces
• Weakest force
• Instantaneous Dipole
• Electrons in constant
motion
• No permanent positive/
negative region
• Strength of force depends
on total # of electrons
8. London Forces
• Weakest force
• Instantaneous Dipole
• Electrons in constant
motion
• No permanent positive/
negative region
• Strength of force depends
on total # of electrons
9. London Forces
• Weakest force
• Instantaneous Dipole
• Electrons in constant
motion
• No permanent positive/
negative region
• Strength of force depends
on total # of electrons
10. London Forces
• Weakest force
• Instantaneous Dipole
• Electrons in constant
motion
• No permanent positive/
negative region
• Strength of force depends
on total # of electrons
11. London Forces
• Weakest force
• Instantaneous Dipole
• Electrons in constant
motion
• No permanent positive/
negative region
• Strength of force depends
on total # of electrons
12. London Forces
• Weakest force
• Instantaneous Dipole
• Electrons in constant
motion
• No permanent positive/
negative region
• Strength of force depends
on total # of electrons
13. London Forces
• Weakest force
• Instantaneous Dipole
• Electrons in constant
motion
• No permanent positive/
negative region
• Strength of force depends
on total # of electrons
14. London Forces
• Weakest force
• Instantaneous Dipole
• Electrons in constant
motion
• No permanent positive/
negative region
• Strength of force depends
on total # of electrons
15. London Forces
• Weakest force
• Instantaneous Dipole
• Electrons in constant
motion
• No permanent positive/
negative region
• Strength of force depends
on total # of electrons
16. London Forces
• Weakest force
• Instantaneous Dipole
• Electrons in constant
motion
• No permanent positive/
negative region
• Strength of force depends
on total # of electrons
17. London Forces
• Weakest force
• Instantaneous Dipole
• Electrons in constant
motion
• No permanent positive/
negative region
• Strength of force depends
on total # of electrons
18. London Forces
• Weakest force
• Instantaneous Dipole
• Electrons in constant
motion
• No permanent positive/
negative region
• Strength of force depends
on total # of electrons
19. Permanent Dipoles
• More durable than
London Force
• Permanent imbalance
of e- in molecule
• Positive and
Negative end
• Example: Acetone Acetone
20. Hydrogen Bonds
• Strongest of all of the
intermolecular forces
• Must have...
• H-N; H-F; or H-O
• N, F, O very high EN values
• Higher than expected BP, MP Water
22. Are There Exceptions?
• Yes, the total number of intermolecular
forces present is very important
• Some waxes (CH -CH -CH ....CH ) have
3 2 2 3
very high melting points despite having only
London Forces
• SbH has a higher BP than H O
3 2
• How can this be explained?
23. A Few Closing Questions...
• Describe the bonding in CH3Cl?
• CH3-CH2-CH2-OH
• What about CH3-CH2-CH2-CH2-CH3?
• What force holds the base pairs (C,G,A,T)
together in DNA?
• Covalent bonds? London forces? Hydrogen
Bonds?
• Why?
