Water

Diagram of a water molecule

H2O

Water is arguably the most important molecule in the universe. It has many amazing properties which make it a very useful and important molecule for life. It also has many fascinating and odd properties which are very interesting to study.

Dihydrogen monoxide, H2O is an odorless, tasteless compound that appears colourless in small quantities however when in a large quantity can appear slightly blue in colour. The molecule itself has two hydrogen atoms bonded to one central oxygen.

The celsius  temperature scale was based on the melting and evaporating points of water, (0oC freezing point and 100oC the evaporating point) this use of this 100 degrees gives rise to the term centigrade. Water is in fact a very odd molecule as its boiling and melting point are much higher than for other similar compounds. This is due to the electronegativity (the ability of an atom to pull electrons toward it) of the oxygen atom, this make the bond very polar (the oxygen is a little more negative and the hydrogen is a little more positive rather than completely neutral).

Hydrogen bonding occurs

Hydrogen Bonding occurs between a slightly positive hydrogen and a slightly negative oxygen

As opposites attract when water molecules pass each other they are much more strongly attracted to each other than other similar molecules, this increased attraction raises the boiling and melting points of water. This intermolecular attraction is known by scientists as hydrogen bonding.

This hydrogen bonding phenomenon gives rise to several major properties of water, most notably that ice floats in water, the only non-metal compound whose solid is less dense than the liquid! Indeed at 0oC ice has a density of 0.9167 g cm-3 whereas water at 0oC is in fact 0.9998 g cm-3. This is down to the hydrogen bonding within solid water which means the solid forms a lattice structure increasing the size of the crystal. In short, water expands as it freezes lowering the density of the material allowing it to float.

What makes our planet so special?

Is there life out there? If there isn’t any water, its unlikely!

As we regularly hear in the news scientists (astronomers) looking for life on other planets often get very excited when they discover that planets have water on them, the reason is that within our ecosystem on earth every living organism requires water. Not only does it help transport chemicals around the body but it is incredibly important as a solvent. Reactions in the body often happen in water. Without water cells would not be able to release energy from glucose or carry out any other reaction. On earth water exists in all three states obviously as a liquid (in the oceans, streams, rivers or as anyone from Wales will tell you as rain!) as a solid, or ice, and finally as water vapour, surprisingly water can is often the third most abundant compound in the atmosphere ranging from 1-5%. Amazingly water is very rarely completely pure as it often has many gasses or metals dissolved in it.

A droplet of water

A drop of water

When you turn on your tap at home the water running out has a variety of chemicals dissolved in it. This varies depending on the area that you live, for example many English water suppliers add fluoride to the water however Welsh Water refuse, this has been an area of much contention throughout the years. Many water supplies also contain calcium carbonate which can cause fur or scale in kettles, boilers and other water heating devices. This is exactly the same stuff that appears in caves as stalactites and stalagmites are both residues of calcium carbonate which is left by individual droplets of water

All in all, water in an amazing molecule, and as recent news items have pointed out, a very important resource in the world. Next time you turn on the tap or run a bath just think for a moment about the amazing molecules that you have access to, and without which life simply couldn’t have started!

Further Links:
Wikipedia
Sigma-aldrich
allaboutwater.org
Water Treatment UK