Intermolecular Forces Flashcards
Name 3 types of intermolecular bonds.
- Van der Waals dispersion forces
- Dipole-dipole forces
- Hydrogen bonds
Between what type of molecule do Van der Waals forces occur?
They occur between all molecules.
How do Van der Waals forces arise?
- Electrons are mobile, so at any one instant their arrangement can result in temporary dipoles within a molecule.
- This molecule can induce dipoles in neighbouring molecules
- There is attraction between these dipoles.
Between what type of molecule do dipole-dipole forces occur?
Between molecules with permanent dipoles.
How to dipole-dipole forces arise?
Molecules with permanent dipoles attract each other. Polar molecules have a partial negative end and a partial positive end. The partial positive end of a polar molecule is attracted to the partially negative end of another.
What determines whether molecules are polar or not?
- Symmetry of the molecule
- The electronegativity differences between atoms in a molecule resulting in polar bonds.
What affects the size of Van der Waals forces?
The size of Van der Waals forces increases with the number of electrons present. So atoms or molecules with large atomic/molecular masses produce stronger V.D.W forces than atoms/molecules with smaller atomic/molecular masses.
What effect to intermolecular forces have on the boiling points of molecules?
They increase the boiling points.
What 2 conditions have to be met for hydrogen bonds to be formed?
- The hydrogen has to be attached directly to one of the most electronegative elements (N,O,F)
- The element bonded to the hydrogen has to have at east one active lone pair.
Why is ice less dense than water?
-In ice, the water molecules arrange themselves in such a way as to maximise the amount of hydrogen bonding between them. This results in the molecules being held further apart than they would be in water.
