IMFs: H Bonds, Polarizability, and Dispersion Forces Flashcards
What is a hydrogen bond?
A dipole-dipole force between molecules that have an H atom bonded to N, O, or F
For a hydrogen bond to exist, do the N, O, or F need lone pairs?
Yes
Is a hydrogen bond stronger or weaker than other dipole-dipole forces?
Stronger
Does CH3-CH2F form hydrogen bonds with itself?
No, because F is bonded to C, not H
Does CH3-CH2F form hydrogen bonds with water?
Yes, because the F has lone pairs. An H bond forms between the F and the H in water.
Does CH3-CH2-NH2 form hydrogen bonds with itself?
Yes, because H is bonded to N, which has lone pairs
Does CH3-OH form hydrogen bonds with itself?
Yes, because H is bonded to O, which has lone pairs
Does a substance with hydrogen bonds have a high or low boiling point?
Very high boiling point because of its strong IMFs.
Which has a lower boiling point, HF or HCl?
HCl because it lacks hydrogen bonds
What happens when an electric field distorts the electron cloud of a polar molecule?
It enhances the existing dipole moment
What happens when an electric field distorts the electron cloud of a nonpolar molecule?
It induces a temporary dipole moment
What is polarizability?
How easy it is to distort a particle’s electron cloud
What are the two types of induced dipole forces?
Ion-induced and dipole-induced
Are smaller or larger particles more polarizable?
Larger
On the periodic table, where is the polarizability the highest?
Down and to the left
Why does polarizability increase down a group?
Larger electron clouds are distorted more easily
Why does polarizability decrease across a period?
Atoms are smaller (less polarizable) due to higher effective nuclear charge
Are cations or anions more polarizable? Why?
Anions because they are larger
What are London dispersion forces?
Intermolecular attractions due to instantaneuous polarizations of electron clouds.
What causes instantaneous dipoles to form in London dispersion forces?
Electron motion. When electrons move, they may, for an instant, occupy one side of the atom, which creates a momentary partial charge.
Which molecules, atoms, and ions exhibit London dispersion forces?
All of them
Which molecules have stronger dispersion forces?
Molecules that are more polarizable (and therefore, larger)
Is a molecule with greater surface area more or less polarizable? Why?
More polarizable because there are more points at which dispersion forces can act.
Do molecules with less surface area have higher or lower boiling points?
Lower boiling points because they experience less intermolecular attraction.
Rank the four IMFs from strongest to weakest.
Ion-dipole
Hydrogen bond
Dipole-dipole
London dispersion forces
Which is more polarizable, Ne or I2?
I2 because it is larger.
Which has weaker dispersion forces, He or Cl2?
He because it is smaller (less polarizable).
A substance with lower molar mass typically has a low boiling point. What is an exception to this?
If the substance forms hydrogen bonds, it can have a higher boiling point despite low molar mass
In a sample of an ionic compound, what is the strongest IMF?
Ionic bonding forces
Which are stronger, dipoles or induced dipoles?
Dipoles
