1. Intermolecular Forces 1
Mr. Tsigaridis

2. Intermolecular Forces
H2O and H2S both have a similar molecular shape based on their Lewis Structures (Angular)
The main difference is that H2O is a liquid at room temperature and H2S is a gas at room temperature
H2O Boiling Point oC
H2S Boiling Point oC

3. Why the Difference?
Everything that you have learned about bonding has been about intramolecular forces (within molecules)
These are the bonds that build molecules and are responsible for the chemical properties of that compound
The physical properties are influenced by the intermolecular forces (between molecules)

4. Why the Difference?
Even though water and sulfur dioxide are the same size and shape, water’s ability to hydrogen bond allows the forces between molecules to be stronger and therefore hold the molecules together more strongly

5. Johannes Van Der Walls
These types of interactions were extensively studied the Dutch theoretical physicist Johannes Van Der Walls
Intermolecular forces in fact are usually called Van Der Walls forces
These forces are responsible for the physical properties of compounds and molecules

6. Van Der Walls Forces
They are classified into 5 characteristic groups each one with its own unique characteristic and effect
Dipole - Dipole Forces
Hydrogen Bonding
Ion – Dipole Forces
Induced Dipole Forces
Dipole Induced Dipole Forces
Ion Induced Dipole Forces
London Dispersion Forces

7. Dipole-Dipole Forces
In the liquid state, polar molecules (like H2O) will align their oppositely charged polar regions to one another
The attraction by these polar regions is what we call the dipole-dipole force

8. Hydrogen Bonding
Hydrogen bonding is a special type of dipole- dipole force that involves a hydrogen being sandwiched in between two very electronegative elements
Since there is a large difference in electronegativity between the element and the hydrogen, a very strong dipole interaction will exist

9. Hydrogen Bonding
Notice that the hydrogen that is attached to the oxygen is attracted to the nitrogen in the ammonia through a hydrogen bond

10. FONClBr
FONClBr is a Mnemonic device that can be used to help determine
F – Fluorine
O - Oxygen
N - Nitrogen
Cl - Chlorine
Br - Bromine
If the hydrogen is sandwiched between any of these two elements, it has the ability to form hydrogen bonds