3. Polar Interactions

Question 1

What is a polar molecule?

Answer 1

An electrically neutral molecule (one that carries no net charge) that has an electric dipole moment.

Question 2

Define electric dipole moment

Answer 2

A measure of the separation of positive and negative electrical charges within a system.

Question 3

What is a zwitterion?

Answer 3

A water-soluble polar molecule. The polarity of this molecule depends on its local environment so it is only polar in water.

Question 4

What is a dipolar ion?

Answer 4

A molecule with a net charge and a dipole moment.

Question 5

Give the equation for the electric field generated by an electric dipole

Answer 5

E = electric field
q = charge
d = charge separation distance
ε = dielectric constant
x = position

Question 6

Give the equation for the electric dipole moment

Answer 6

p = electric dipole moment
q = charge
d = charge separation distance

Question 7

Give the equation for the potential energy of a dipole in an electric field

Answer 7

U = potential energy
p = electric dipole moment
E = electric field

Question 8

Atoms and molecules are ________ by external electric fields because they cause opposite charges to move in different directions.

Answer 8

Polarised

Question 9

Give the equation that relates the dipole moment of an atom/molecule to the external applied electric field

Answer 9

p = dipole moment
α = polarisability
E = external electric field

Question 10

Give the equation for the polarisability of an atom/molecule in an applied external field

Answer 10

α = polarisability
ε = permittivity
d = separation distance between +ve and -ve components

Question 11

What are dispersion forces?

Answer 11

Interactions that act between all atoms and molecules. They arise as the result of temporary local fluctuations in charge density of atoms/molecules and always result in an attractive force between the atoms.

Question 12

Give 2 other names for dispersion forces

Answer 12

• London forces
• Van der Waals forces