module 2: 6.3 intermolecular forces

Question 1

define the term intermolecular forces

Answer 1

they are weak interactions between dipoles of DIFFERENT molecules.

Question 2

3 main categories of intermolecular forces

Answer 2

• induced dipole-dipole interaction (London forces)
• permanent dipole-dipole interactions
• hydrogen bonding

Question 3

how do induced dipole-dipole interactions (London forces) occur

Answer 3

1. movement of electrons produces a changing dipole in a molecule
2. at any instant, an instantaneous dipole will exist, but its position is constantly shifting
3. the instantaneous dipole induces a dipole on a neighbouring molecule
4. the induced dipole induces further dipoles on neighbouring molecules, which then attract one another

Question 4

the strength of induced dipole-dipole interactions (London forces)

Answer 4

• the larger the instantaneous and induced dipoles
• the greater the induced dipole-dipole interactions
• the stronger the attractive forces between molecules

Question 5

what interactions are van der Waals’ forces used for

Answer 5

both permanent and induced dipole-dipole interactions.

Question 6

define the tern simple molecular substance

Answer 6

a simple molecular substance is made up of simple molecules

Question 7

properties of simple molecular substances

Answer 7

low melting point and boiling point due to weak intermolecular forces breaking (covalent bonds don’t break)

Question 8

solubility of simple molecular substances

Answer 8

non-polar simple molecular substances tend to be SOLUBLE in NON-POLAR solvents
simple molecular substances tend to be INSOLUBLE in POLAR solvents

Question 9

solubility of polar simple molecular substances

Answer 9

POLAR covalent substances may dissolve in polar solvents as the polar solute molecules and the polar solvent molecules can attract each other

Question 10

the conductivity of simple molecular substances

Answer 10

they are non-conductors of electricity

- due to no mobile charged particles in simple molecular structures