Intermolecular Forces

Question 1

Which substances have intermolecular forces between molecules?

Answer 1

Simple molecules

Question 2

Are intermolecular forces strong or weak?

Answer 2

Weak

Question 3

What are the three types of intermolecular forces?

Answer 3

Hydrogen bonding, Permanent dipole-dipole, Induced dipole-dipole

Question 4

Which is the strongest type of intermolecular force?

Answer 4

Hydrogen bonding

Question 5

Which is the weakest type of intermolecular force?

Answer 5

Induced dipole-dipole

Question 6

When is a molecule non-polar?

Answer 6

Molecule is symmetrical,
Dipoles cancel out

Question 7

When is a molecule polar?

Answer 7

Molecule is not symmetrical.
Dipoles do not cancel out.

Question 8

When substances with a simple molecular structure are melted or boiled what is broken?

Answer 8

Weak intermolecular forces are broken

Question 9

Do simple molecules have a high melting point or a low melting point?

Answer 9

Low. The weak intermolecular forces between molecules are broken.

Question 10

What is the strongest intermolecular force between polar molecules?

Answer 10

Permanent dipole-dipole

Question 11

What is the strongest intermolecular force between non-polar molecules?

Answer 11

Induced dipole-dipole

Question 12

What is the strongest type of intermolecular force between simple molecules that have a H bonded to an N, O or F?

Answer 12

Hydrogen bonding

Question 13

How do you know if simple molecules have hydrogen bonding between them?

Answer 13

• They have a H bonded to an N, O or F.
• A lone pair of electrons on the fluorine, oxygen or nitrogen

Question 14

Hydrogen bonding is the strongest type of intermolecular force, true or false?

Answer 14

True

Question 15

Induced dipole-dipole is the weakest type of intermolecular force, true or false?

Answer 15

True

Question 16

Explain how is an induced dipole-dipole intermolecular force is formed between 2 non-polar molecules.

Answer 16

• Random movement of electrons in one molecule (atom) leads to an…
  Uneven distribution of electron, creating a…
• Temporary dipole in one molecule (atom). This…
• Induces a dipole in a neighboring molecule (atom).
• Dipoles attract

Question 17

If the strongest intermolecular force between molecules is Hydrogen bonding, which other intermolecular forces do they also have?

Answer 17

Permanent dipole-dipole and Induced dipole-dipole

Question 18

If the strongest intermolecular force between molecules is permanent dipole-dipole, which other intermolecular force do they also have?

Answer 18

Induced dipole-dipole

Question 19

Non-polar molecules only have induced dipole-dipole forces between molecules, true or false?

Answer 19

True

Question 20

What increases the strength of induced dipole-dipole forces?

Answer 20

More electrons
More surface contact area

Question 21

Which has stronger induced dipole-dipole, Cl2 or Br2 ?

Answer 21

Br2. It has more electrons

Question 22

Which has stronger induced dipole-dipole, F2 or I2 ?

Answer 22

I2. It has more electrons

Question 23

Which has stronger induced dipole-dipole, S8 or P4 ?

Answer 23

P4. Bigger molecules so has more electrons

Question 24

Which has stronger induced dipole-dipole, C3H8 or C4H10?

Answer 24

C4H10. Bigger molecules so has more electrons

Question 25

Which has a higher boiling point, Cl2 or Br2 ?

Answer 25

Br2. It has more electrons so stronger induced dipole-dipole.

Question 26

Which has a higher boiling point, F2 or I2 ?

Answer 26

I2. It has more electrons so stronger induced dipole-dipole.

Question 27

Is CCl4 polar or non-polar molecule? (Clue: Draw it out with partial charges.)

Answer 27

Non-polar
Symmetrical molecule
Dipoles cancel out

Question 28

Is CHCl3 polar or non-polar molecule? (Clue: Draw it out with partial charges.

Answer 28

Polar
Not symmetrical molecule
Dipoles do not cancel out

Question 29

Why does HBr have a higher boiling point than HCl?

Answer 29

Both polar molecules
Strongest intermolecular force is permanent dipole-dipole.
They will also have induced dipole-dipole.
HBr has more electrons that HCl, stronger induced dipole-dipole attraction.

Question 30

Why does HI have a higher boiling point than HCl?

Answer 30

Both polar molecules
Strongest intermolecular force is permanent dipole-dipole.
It will also have induced dipole-dipole.
HI has more electrons that HCl, stronger induced dipole-dipole attraction.

Question 31

Why does HI have a higher boiling point than HF?

Answer 31

Both polar molecules
Strongest intermolecular force is permanent dipole-dipole.
It will also have induced dipole-dipole.
HI has more electrons that HF, stronger induced dipole-dipole attraction.

Question 32

Would the molecule be polar or non-polar if it is symmetrical and
dipoles cancel out?

Answer 32

Non-polar

Question 33

Would the molecule be polar or non-polar if it is not symmetrical and
dipoles do not cancel out?

Answer 33

Polar

Question 34

Which molecules would have a higher melting point?
Molecules with hydrogen bonding between molecules or
Molecules with Induced dipole-dipole forces between molecules.

Answer 34

Molecules with hydrogen bonding between molecules. Hydrogen bonding would require more energy to break the intermolecular forces.

Question 35

Correct the following statement:
Simple molecules have low melting points as they have intermolecular forces which require less energy to break the bonds

Answer 35

Simple molecules have low melting points as they have intermolecular forces BETWEEN MOLECULES which require less energy to break the FORCES

Question 36

Correct the following statements:
Cl₂ has a lower boiling point than HF. Cl₂ has induced dipole-dipole forces and HF has hydrogen bonding. induced dipole-dipole is weaker than hydrogen bonding. Less energy is require the break the bonds between Cl₂.

Answer 36

Cl₂ has a lower boiling point than HF. Cl₂ has induced dipole-dipole forces between molecules and HF has hydrogen bonding between molecules. induced dipole-dipole forces are weaker than hydrogen bonding. Less energy is require the break the forces between Cl₂.

Question 37

How does permenant dipole-dipole arise

Answer 37

• Difference in electronegativity leads to bond polarity
  Dipoles don’t cancel therefore the molecule has an overall permanent dipole
• There is an attraction between ∂+ on one molecule and ∂− on another