Water is Strange - This is my blog now

Water is Strange

17 May 2026

Did you know how extraordinary water is? This substance that we (living in privileged countries) mostly take for granted which is so ubiquitous on this planet we live on? I am not talking about the philosophical aspects, how soothing it is to sit by the sea and listen to the waves, or how tranquil and content it can make you feel to sit at a pond on a warm summer's day and let your feet hang into the water. Sure, it can sustain us, make us clean and all that, but water is, physically speaking incredibly strange.

Density

As you'll know, water comes in three(ish) phases: solid, liquid and gaseous (actually, there's lots of additional phases in the solid state but we'll not concern ourselves with that here). Which one you're dealing with depends on the temperature and pressure. Here is a stylized phase diagram of water:

At 1 atm (air pressure at sea level) heating up solid water will first transform it into a liquid and then a gas, so far so standard. But notice that the line separating the solid and liquid forms of water has a negative slope. This is highly unusual and means that liquid water is more dense than solid water. Consequently, if you apply increasing pressure to ice, it will melt. On the other hand, upon freezing the density of water decreases by about 9%, which can exert enormous pressure and is the reason why water pipes burst when frozen and why it's not a good idea to put beer in the freezer for prolonged periods of time.

This has interesting consequences. Ice floats on top of liquid water and acts as a temperature shield for the water below which is what keeps fish living in lakes alive during the winter. This also plays an important part in the thermohaline circulation which lets water circulate around the globe.

Hydrogen bonding

Water is a triatomic molecule, consisting of two hydrogen atoms and one oxygen atom bound together to form an angle of 104.5°. Because water is polar, different water molecules interact with each other, specifically, they form so-called hydrogen bonds where a Hydrogen atom of one molecule bonds with the oxygen atom of another molecule. While these are not as strong as full covalent bonds (this is what one might call a chemical bond. It hurts me a little to write this but it's close enough and bonding theory is incredibly complex), they are much stronger than just pure electrostatic interactions.

This has consequences: because of the aforementioned interactions water molecules are relatively tightly bound together. This means that it takes more energy to pry them apart again, resulting in a few very important properties of water:

High melting point

High boiling point

High specific heat capacity

High surface tension

High capillary forces

What do I mean by high? Consider the following graph:

Chemists like finding trends in related chemical compounds which is what this is. This shows the boiling point of related compounds (elements surrounding oxygen bound to hydrogen), both from adjacent rows or periods in the periodic table of elements. There is a lot that can be gleaned from these few data points but let me just point out this: of all the elements we see here, oxygen is clearly the one that forms the hydrogen compound with the strongest intermolecular hydrogen bonds, and by a large margin. Clearly there is something unique about this particular molecule.

OK, but what does this all matter? Consider the following: water occurs in solid, liquid and gaseous form on earth because surface pressure and temperature are close to its triple point. This is the point in the phase diagram above where the sections for all three phases meet, for water this is at 0.006 atm and 0 °C (the zero point of the Celsius scale is defined this way). This is only possible because the melting and boiling point of water is much higher than one might expect looking at comparable compounds. And since water is instrumental for our existence, life on earth as we know it is only possible because of this property of water.

Another point: water has the highest specific heat capacity (the amount of energy to heat up a substance by 1 °C, or K, if you prefer) of all naturally occurring liquids, except ammonia (which has a much lower boiling point). This makes it well-suited to regulate temperature and move around heat and energy around the globe. Which is what the oceans actually do. Fancy that.<br>Do you own a pool? This is the reason why it takes ages to heat it up (or cool it down) and why the electricity bill is seriously impacted, if you do.

Water tends to climb up a narrow tube in defiance of gravity which many plants and trees rely on for their water uptake, they wouldn't survive otherwise. Sure, if water were different, plants would surely have evolved differently. Still, this showcases how strongly life on earth is connected to the peculiarities of one substance.

There is a lot more to the hydrogen bonding of...