It’s snowing!!!!

So it’s that cold time of year when we should expect a bit of travel disruption and shouldn’t leave the house without hat, gloves and scarves. And as it’s the first time I’ve had to scrape ice off my car in the morning I thought it was about time I turned the snow machine on and let chemstuff.co.uk be a little festive!

It’s also a good excuse to look at the chemistry of snow

Snow is of course formed in clouds where the temperature is less that 0oC (or 273K) this means that the water vapour present will start to crystallise and form a snowflake. Crystals are structures with a very high level of order and we can see this when we look at a snowflake in a lot of detail. Whilst they are not always absolutely symmetrical, snowflakes do follow similar patterns. This is because a snowflake’s shape reflects the internal order of the water molecules. Water molecules in the solid state, such as in ice and snow, form weak bonds (called hydrogen bonds) with one another. These ordered arrangements result in the symmetrical, hexagonal shape of the snowflake. During crystallization, the water molecules align themselves to maximize attractive forces and minimize repulsive forces. Consequently, water molecules arrange themselves in predetermined spaces and in a specific arrangement. Water molecules simply arrange themselves to fit the spaces and maintain symmetry.

As we know water and ice often appear clear and colourless but snow appears to be white, this is because snowflakes have so many surfaces, owing to its crystal structure, that reflect light and scatters most of the rays that hit it.

So whether we have a white christmas this year, or not. If you see a snowflake, why not start to appreciate some of the chemistry behind it!