Ice

When water converts into ice it does so at its freezing point.

At sea level water freezes at 0 degrees Celsius, but this can vary depending on altitude and air pressure.

Creative Commons Image SuburbanSlice via Flickr
Ice melting [Image: suburbanslice under CC-BY-NC-ND licence]

At its freezing point, water becomes solid ice. As water cools, the molecules lose kinetic energy and start to slow down.

The hydrogen bonds hold the molecules together in a regular lattice, and the solid state is formed.

Because the molecules are close to each other and bound together tightly, ice has a defined volume and shape, both characteristic features of solids.

Most natural ice has a hexagonal structure, with each molecule bonding to four others.

Unlike most solid forms of liquids, ice is less dense than liquid water.

This is because, in ice, the hydrogen bonds hold the molecules in a lattice structure, where the distance between each molecule is greater than in liquid water.

The lower density of ice means that it floats in water.