Intermolecular Forces

Question 1

What is an intramolecular force?

Answer 1

bonding forces that exist within each molecule and influence the chemical properties of the substance

Question 2

What is an intermolecular force?

Answer 2

non-bonding force that exist between the molecules and influence the physical properties of the substance

Question 3

What are the different kinds of intermolecular forces?

Answer 3

1. dipole-dipole
2. (ion-dipole forces)
3. London dispersion forces
4. hydrogen bonding

Question 4

dipole = what

Answer 4

polar molecule

Question 5

what is dipole-dipole force?

Answer 5

the electrostatic attraction between the ends when dipoles change their direction so that their oppositely charged ends are near to one another.

the electrostatic attraction between the molecules with permanent dipoles

Question 6

The stronger a dipole or ΔEN in a molecule….

Answer 6

the stronger the dipole-dipole force between the molecules

Question 7

what is an ion-dipole force?

Answer 7

the force of attraction between an ion and a polar molecule.

The charge of the ion will attract the opposite partial charge of the dipole.

Question 8

what is the weakest intermolecular force between non polar molecules?

Answer 8

Londen dispersion forces (LDF)

Question 9

What are London dispersion forces?

Answer 9

a temporary attractive force that results when the electrons in two adjacent atoms occpy positions that make the atoms form temporary dipoles.

Question 10

both polar and non polar molecules experience London dispersion forces

Question 11

Explain the temporary dipole in London dispersion forces.

Answer 11

• electrons are constantly moving
• at any given time there may be an unequal distribution of electrons forming a temporary dipole
• the temporary dipole will cause the electrons in another molecule to be repelled. This will cause an induced dipole
• (one atom becomes more e- positive and the other becomes more e- negative)
• there is now on average a stronger attractive force between molecules than repulsive.

Question 12

What are the two factors that influence the strength of london dispersion forces?

Answer 12

• number of electrons in the molecule
• the effective surface area of the molecule

Question 13

How does the number of electrons in a molecule impact the London Dispersion forces?

Answer 13

the greater the number of electrons, the stronger the London Dispersion force.

Question 14

How does the effective surface area of the molecule impact the Londond DIspersion Forces?

Answer 14

the greater the surface area for contact between molecules, the stronger the London dispersion

atoms have to be roughly the same size for this to work.

Question 15

What is a Hydrogen Bond?

Answer 15

a very strong dipole-dipole force

Question 16

What is hydrogen bonding the result of?

Answer 16

Hydrogen bonding results between the interaction of the lone pair of one atom with the hydrogen atom of another molecule.

Basically, the large ΔEN that exists between a hydrogen atom and another creates a strong dipole

Question 17

Where MUST the lone pair in a hydrogen bond come from? What should the other molecule involved have?

Answer 17

N (nitrogen), O (oxygen), or F (fluorine)

the other molecule involved should have at least one lone pair

Question 18

more lone pairs in a hydrogen bond == ….

Answer 18

stronger hydrogen bonds

Question 19

Chloring is too big to form hydrogen bonds

Question 20

what is the strongest of the intermolecular forces?

Answer 20

hydrogen bonding

Question 21

How does hydrogen bonding affected the properties of water?

Answer 21

1. it is responsible for water’s high melting and boiling point for its size
2. adhesive and cohesive properties (hydrogen bonding allows water molecules to stick to each other and surfaces, aids in transportation of water from roots to leaves in plants)
3. high specific heat capacity ( heat is absorbed when hydrogen bonds break and is released when hydrogen bonds form, helping minimize temperature fluctuations in oceans etc.
4. high heat of vaporization (sweating)
5. water is the solvent of life
6. slid form of water is less dense than its liquid form, which allows marine life to survive in frozen lakes

Question 22

Melting point is a measure…

Answer 22

of the difference in strength of the forces between particles between the solid and liquid state.

Question 24

melting point and atomic size

Answer 24

the larger the atomic size, the more energy it requires to melt the molecule

the larger the size, the more electrons there are moving randomly around, so the larger the London Dispersion Forces occuring between each molecule
- the sheer amount of LDF outweighs the “stronger” dipole-dipole force