Topic 2.2.5 - Intermolecular interactions

Question 1

What happens to electrons when hydrogen is bonded to a highly electronegative atom?

Answer 1

The bonding pair of electrons is drawn towards the more electronegative atom.

Question 2

Definition of hydrogen bonding.

Answer 2

Electrostatic attraction between hydrogen atoms bonded to small, strongly electronegative atoms and the lone pair electrons on the electronegative atoms.

Question 3

What is stronger,
An intermolecular hydrogen bond or London forces?

Answer 3

Intermolecular hydrogen bond

Question 4

Why do H2O, NH3 and HF have a high boiling point?

Answer 4

N,O and F are highly electronegative atoms.
They form hydrogen bonds which are much stronger than London forces.
More energy needed to break bonds.

Question 5

Why does H2O have a higher boiling point than HF and NH3?

Answer 5

H2O can form 2 hydrogen bonds per molecule. (2 H in each molecule)
Others can only form 1.

Question 6

In terms of hydrogen bonds, why does ice have a lower density than water?

Answer 6

Each H2O molecule is tetrahedrally bonded to 4 other H2O molecules by hydrogen bonds.
This insulates water below preventing complete solidification.

Question 7

How do London forces arise?

Answer 7

Electrons move at high speeds on orbitals.
It’s possible for more electrons to be on one side of a molecule.
A dipole forms when one side is slightly positive n the other negative.
A dipole in one molecule can induce a dipole in a neighbouring one.

Question 8

How do permanent dipole-dipole interactions arise?

Answer 8

Molecules containing polar bonds
Extra attraction between dipoles
Higher boiling points

Question 9

What happens to the strength of a London force is there are more electrons?

Answer 9

Strength increases