Earlier, Joe asked in an all-staff email:

“Did you put a 2 liter bottle of sparkling water in the freezer to get it cold? Did you forget to take it out? Well it exploded. Please clean up the glass ASAP.”

I’m glad you raised that, Joe as physics is an important of what we do.

Water is the only liquid which expands when it freezes.

Usually, substances shrink as they cool and water is no exception, for the most part, BUT BUT BUT when it cools, it reaches its maximum density (i.e. the smallest distance between molecules) at 34 degrees F and between 34 degrees F and 32 degrees F, it actually expands slightly.

At 32 degrees F, ice forms and there is expansion as the water freezes.

The reason it expands is that the water molecules are re-arranged during freezing to form the crystal structure of ice. This new structure takes up slightly more space than it did when it was still liquid.

The expansion has to do with the peculiar molecular structure of water, which looks like this:

O
/ \
H H

Water binds together because oxygen atoms are attracted by each of the nearby hydrogen atoms. When in the liquid state, the binding is weak, but when solid, the bonds become quite strong, and constrain how the molecules may arrange themselves as a crystal. In its liquid state, the molecules are free to roam around wherever they wish. However, in its frozen state, the water molecules form a hexagon giving the beautiful six-sided snowflakes with which we are all familiar. In this state, the molecules line up like this:

H2O
/ \
H2O H2O
| |
H2O H2O
\ /
H2O

The lines represent the molecular bonds holding the molecules in place. NB: the center is empty. In its liquid form, with the molecules moving about freely, you will find an H2O molecule in the center of such a structure, but not in its solid state. So, a given amount of water will use up more room as ice than as a liquid, because of the empty space that appears as it freezes. Thus, ice is less dense and it floats.