IMFs: H Bonds, Polarizability, and Dispersion Forces

Question 1

What is a hydrogen bond?

Answer 1

A dipole-dipole force between molecules that have an H atom bonded to N, O, or F

Question 2

For a hydrogen bond to exist, do the N, O, or F need lone pairs?

Answer 2

Yes

Question 3

Is a hydrogen bond stronger or weaker than other dipole-dipole forces?

Answer 3

Stronger

Question 4

Does CH3-CH2F form hydrogen bonds with itself?

Answer 4

No, because F is bonded to C, not H

Question 5

Does CH3-CH2F form hydrogen bonds with water?

Answer 5

Yes, because the F has lone pairs. An H bond forms between the F and the H in water.

Question 6

Does CH3-CH2-NH2 form hydrogen bonds with itself?

Answer 6

Yes, because H is bonded to N, which has lone pairs

Question 7

Does CH3-OH form hydrogen bonds with itself?

Answer 7

Yes, because H is bonded to O, which has lone pairs

Question 8

Does a substance with hydrogen bonds have a high or low boiling point?

Answer 8

Very high boiling point because of its strong IMFs.

Question 9

Which has a lower boiling point, HF or HCl?

Answer 9

HCl because it lacks hydrogen bonds

Question 10

What happens when an electric field distorts the electron cloud of a polar molecule?

Answer 10

It enhances the existing dipole moment

Question 11

What happens when an electric field distorts the electron cloud of a nonpolar molecule?

Answer 11

It induces a temporary dipole moment

Question 12

What is polarizability?

Answer 12

How easy it is to distort a particle’s electron cloud

Question 13

What are the two types of induced dipole forces?

Answer 13

Ion-induced and dipole-induced

Question 14

Are smaller or larger particles more polarizable?

Answer 14

Larger

Question 15

On the periodic table, where is the polarizability the highest?

Answer 15

Down and to the left

Question 16

Why does polarizability increase down a group?

Answer 16

Larger electron clouds are distorted more easily

Question 17

Why does polarizability decrease across a period?

Answer 17

Atoms are smaller (less polarizable) due to higher effective nuclear charge

Question 18

Are cations or anions more polarizable? Why?

Answer 18

Anions because they are larger

Question 19

What are London dispersion forces?

Answer 19

Intermolecular attractions due to instantaneuous polarizations of electron clouds.

Question 20

What causes instantaneous dipoles to form in London dispersion forces?

Answer 20

Electron motion. When electrons move, they may, for an instant, occupy one side of the atom, which creates a momentary partial charge.

Question 21

Which molecules, atoms, and ions exhibit London dispersion forces?

Answer 21

All of them

Question 22

Which molecules have stronger dispersion forces?

Answer 22

Molecules that are more polarizable (and therefore, larger)

Question 23

Is a molecule with greater surface area more or less polarizable? Why?

Answer 23

More polarizable because there are more points at which dispersion forces can act.

Question 24

Do molecules with less surface area have higher or lower boiling points?

Answer 24

Lower boiling points because they experience less intermolecular attraction.

Question 25

Rank the four IMFs from strongest to weakest.

Answer 25

Ion-dipole Hydrogen bond Dipole-dipole London dispersion forces

Question 26

Which is more polarizable, Ne or I2?

Answer 26

I2 because it is larger.

Question 27

Which has weaker dispersion forces, He or Cl2?

Answer 27

He because it is smaller (less polarizable).

Question 28

A substance with lower molar mass typically has a low boiling point. What is an exception to this?

Answer 28

If the substance forms hydrogen bonds, it can have a higher boiling point despite low molar mass

Question 29

In a sample of an ionic compound, what is the strongest IMF?

Answer 29

Ionic bonding forces

Question 30

Which are stronger, dipoles or induced dipoles?

Answer 30

Dipoles