London Dispersion Forces

Question 1

Why do non-polar moleucles have no permanent separation of charge within bonds?

Answer 1

shared electrons pulled equally by two atoms

Question 2

What do noble gases exist as?

Answer 2

non-polar particles

Question 3

How are london dispersion forces formed?

Answer 3

• electrons behave like mobile clouds of negative charge
• density of cloud may be greater at one moment
• over one region temporary/instantaneous dipole formed
• influences electron distribution in neighbouring atoms
• causes induced dipole weak
• forces of attraction (london forces) occur between opposite ends of two temporary dipoles in molecules

Question 4

london forces are the — form of intermolecular force

Answer 4

weakest

Question 5

the strenght of london forces — with moledulcar size Why?

Answer 5

increases greater number of electrons within a molecule increases probability of dipole developing

Question 6

trend in melting/boiling points in non-polar molecules

Answer 6

• low melting/boiling points
• london forces are only forces that exist between non-polar molecules
• little energy required to break weak london foces and separate molecules from each other

Question 7

hydrogen bonding

Answer 7

attraction when a molecule contains a hydrogen covalently bonded to a very electronegative atom (F, N, O)

Question 8

hydrogen bonding effect on boiling point

Answer 8

makes boiling point much higher