Water is so incredibly important that without it, life as we know it could not exist. Yet it is often taken for granted.
Chemically, water is formed when an atom of Oxygen combines with two atoms of Hydrogen. Oxygen is lacking two electrons to have a complete outer electron shell, and each of the Hydrogen atoms have a single electron, so the combination leads to a stable compound, water.
Water also has some interesting properties. Most people are aware that at sea level, water freezes at 32 degrees Fahrenheit (0 degrees Celsius) and boils at 212 degrees Fahrenheit (100 degrees Celsius). It is some of water's other properties that are the most interesting, though.
For one, water is one of the very few substances that expands when it freezes. This makes frozen water lighter than liquid water, and explains why ice cubes float. It also explains why the Earth is not a frozen ball. If ice sunk, the ice that calves off into the oceans in the form of icebergs would sink to the bottom of the oceans, where the very cold currents would not thaw it out. Over thousands of years, the oceans would gradually fill with ice, which would cause them to become colder and colder, until they were nothing but ice.
Also, water vapor is one of the greenhouse gases, allowing heat in from the sun, but blocking it from easily escaping. Without water vapor in the atmosphere, our planet would again be a frozen ball of ice.
A water molecule has a strong attraction to other water molecules, and this produces a strong "surface tension". This can be seen by pouring water into a glass and looking at the surface at eye level. The water curves up where it contacts the glass, rather than being a totally flat surface. A common classroom experiment to show this chemical property is to carefully place a needle on the surface of the water, parallel to the surface. It will float.
Surface tension also explains why water falling, such as in rain drops, takes on a roughly spherical shape.
Water has another interesting property, owing in part to the shape of the molecule and the way the Oxygen and Hydrogen bonds, as well as due to the surface tension: Liquid water is almost entirely incompressible under normal circumstances. This means that a person falling 10 feet into calm water will actually have about the same force of impact as if they fell the 10 feet onto concrete, which does compress slightly. This is the reason, in fact, that in Olympic high diving competition, jets of water break the surface of the water in the pool.
Water is also a very efficient conductor of both heat and electricity. The old Boy Scout trick of boiling water in a paper cup over an open flame, is made possible because the water conducts the heat more efficiently than does the paper. As for electricity, since the combination of oxygen and hydrogen produces a compound with a balanced electrical charge, electricity, which is a flow of electrons, passes easily through it. The current, however, can cause the bonds between the atoms to break. The result is free oxygen atoms and hydrogen molecules.
One of the useful chemical properties of water is that it combines easily with many elements and compounds. This is vital to life as we know it, however it also means that combining water with sulfur dioxide (SO2) requires only an extra oxygen atom to create sulfuric acid (H2SO4).
While water is so necessary for our continued survival, it is the chemistry of water that makes it useful in so many ways. There might be a tendency to take water for granted, but it really shouldn't be. Studying the properties of water can help us appreciate it, as it should be, and yet may pave the way for new and even more useful compounds..