3.1.3.7 Forces Between Molecules

Question 1

Van der Waals forces

Answer 1

At any moment, oscillations produce an instantaneous dipole
Instantaneous dipoles are created by other dipoles
The dipoles attract each other
Only attractive force between non-polar molecules
Increased VdW forces = increased surface area / increased tesselation/ more electrons / increased chain length / area of contact
They act between all molecules and atoms
More electrons = more charge

Question 2

Dipole dipole forces

Answer 2

Polar molecules line up so that they are attracted to opposing forces
Act only between certain types of molecule
Difference in charge increases the forces, larger difference in electronegativities = stronger the force
Molecules have permanent dipoles which makes the bonds stronger than VdW

Question 3

Hydrogen bonding

Answer 3

Hydrogen bonded to a very electronegative atom (O, N, F)
Electronegative atom must have a lone pair of electrons which will be attracted to the partially positively charged hydrogen atom

Question 4

Why does ice float?

Answer 4

As water cools, the hydrogen bonds spread to hold the negatively charged oxygen atoms apart

Question 5

In which direction do electrostatic forces work?

Answer 5

All directions

Question 6

How do hydrogen bonds form?

Answer 6

The lone pair of the electronegative atom is attracted to the electron deficient hydrogen atom