Water, ice and hydrogen bonding

Oxygen has an electronegativity of 3.5. Hydrogen has an electronegativity of 2.1. So water is polarised δ-δ- δ+δ+ δ+δ+ Polarity of water

δ-δ- δ-δ- δ+δ+ δ+δ+ δ+δ+ δ+δ+ Hydrogen bond Dipoles result in hydrogen bonds between water molecules.

Boiling point Due to H bonds water boils at a much higher temperature than expected.

Capillarity Capillarity is the ability of a liquid to rise up narrow vessels. Due to hydrogen bonds water molecules “stick together” and help haul each other up. Capillarity is used in xylem vessels to help water transport up the stems of plants.

Surface tension is the force needed to break through the surface of a liquid. Due to hydrogen bonds water has a high surface tension. Molecules attract each other.

Allowing pond skaters to skim the surface!

Melting point (freezing point) Due to the strength of the hydrogen bonds ice melts at a much higher temperature than expected.

Water molecules are held together by H bonds in a lattice. NB The lattice is “cage” like, full of “holes” Structure of Ice

Generally liquids become more dense as they cool and freeze. Density of ice But due to all that space in the lattice ice has a lower density than water. So ice floats!

Anti freeze δ-δ- δ-δ- δ+δ+ δ+δ+ The OH groups of ethan 1,2 diol are polarised. This means that they can form H bonds with water molecules. This will slow the growth of the H bonded ice lattice.