2.2.2 Hydrogen bonding

Question 1

define hydrogen bonding

Answer 1

A strong dipole-dipole interaction between an electron deficient hydrogen (𝜹+) and the lone pair of electrons on a highly electronegative atom (O or N) on a different molecule

ignore the commas

H - O : IIIIIII H - O
,,,,,,,I,,,,,,,,,,,,,,,,,,,,,,I
,,,,,,H,,,,,,,,,,,,,,,,,,,,H

The I between the : and the H represent the hydrogen bond

Question 2

when are hydrogen bonds present

Answer 2

they occur in molecules with OH or NH groups

Question 3

describe the strength of hydrogen bonds

Answer 3

They are stronger than London forces and permenant dipole-dipole interactions BUT much weaker than covalent bonds

Question 4

what are the anomalous properties of water

Answer 4

1. relatively high melting and boiling points
2. Ice is less dence than water
3. high surface tension

Question 5

Explain why water has relatively high melting and boiling points

Answer 5

This is caused by the ‘strong’ hydrogen bonds which take more energy to break and so the melting and boiling points are relatively high for a simple molecule
eg. bp of F2 = -188℃
bp of H2O = 100℃

Question 6

Explain why ice is denser than water

Answer 6

Hydrogen bonds hold the water molecules in an open lattice in ice which collapse when melted.

Question 7

explain why water has a high surface tension

Answer 7

this occurs because of the hydrogen bonds.