Intermolecular Forces Flashcards
Describe charge - non-polar interaction.
a field from a charge induces a dipole in a non-polar molecule.
Why do we find the angle averaged interaction for the dipole - non-polar interaction?
The strength of the interaction isn’t enough to mutually orient the molecules.
Van der Waals forces are…
short-ranged and generally attractive
Using the interaction energy between two atoms, how can we find the interaction between molecules (surfaces, spheres)?
Sum over all the atom pairs. Integrate over both volumes, including densities.
Describe the antibonding state.
H atoms have e- with same spin so the spatial wavefunction must be antisymmetric.
Describe the bonding state.
H atoms have e- with opposite spin so the spatial wavefunction must be symmetric.
Which bonding state is lower energy?
Bonding.
What is the need for the Debye screening length?
In solution, the interaction between ions (charges) is screened by other ions. Adds exponential decay in potential energy.
Polar molecules have…
permanent electric dipole moment.
What happens between water molecules?
they orient themselves toward the negative end of another water molecule (Hydrogen atom shared).
Hydrogen bonding occurs between…
polar molecules. Weakly acidic group (O-H,N-H) share H with weakly basic atom (O,N).
What types of particles are hydrophobic?
non-polar molecules. they cannot form hydrogen bonds.
What do hydrophobic molecules do when put in contact with water?
Form aggregates to reduce surface in contact with water.
State the equation for the Hamaker constant.
A = pi^2 rho_1 rho_2 C
What happens to vdW interaction in a polar medium (water, free charges) ?
It is ‘screened’ by the free charges. Effect is reflected by decrease in the Hamaker constant.
