Water: Strange but essential!

Water is a truly fascinating and exceptional molecule. It has unique properties without which life on Earth could not even exist. In the following weeks, we’ll look together behind the curtain and learn more about its uniqueness. Let’s go!

Probably everyone knows its chemical formula – H2O. Water is a small V-shaped molecule consisting of 2 atoms of hydrogen connected to 1 atom of oxygen. Seems simple, right? Water doesn’t look that impressive from its chemical composition. Its colourless and odourless nature may seem boring too, but these 3 atoms hide more than you’d think!

During the last two centuries, chemists all around the world have developed a system to categorize all known liquids and their properties. Well, water doesn’t really care about that.

Imagine yourself on the beach, sun is shining, and you are holding some nice cold drink with ice cubes in it. Wait a moment, shouldn’t the ice cubes be on the bottom of the glass? Why are they floating? Solid material should not be floating on its liquid. Solid wax will sink when you place it on a liquid wax, the same with butter, metals, lava rocks and I could continue like this forever. Water doesn’t behave like that!

Thus, the first unique property of water is the following: When water freezes, it expands, thus has lower density (by ca. 9%), causing the ice to float! That’s why you should never put a full bottle water into freezer, the bottle will break. Water actually reaches its maximum density at 4°C (40°F) and as slowly freezes, it becomes less and less dense. Everything in the universe is pretty lazy and wants to reach the state with lowest possible energy. That's why water molecules in ice arrange into shape that leaves tiny gaps, thus causing the ice to have lower density.

This might seem as a small thing but without this property, the world would be totally different place and without life as we know it.

Floating ice protects all bodies of water from completely freezing! Because bodies of water freeze from the top down, fish, plants and other organisms always have somewhere to survive even during the harhest winter. If ice would sink, suddenly, there is no protection of the water surface and so called “water snow” would occur. Water on the surface would be constantly freezing and falling to the bottom in a form of snow until all water is frozen. That would make the existence of life almost impossible. Some microorganisms could probably survive near some underwater volcanos, but that’s just a theory. It intrigues me to think about all the ifs, could haves, would haves etc. The Earth would be unrecognizable if water didn’t have this weird property but what’s the cause? You shall know soon because this is just a tip of the iceberg.

One of the most strangest things about water is that it exists in normal conditions as a liquid. If water followed the rules, all the water on Earth would exist as only vapour. Oxygen and hydrogen atoms are very light and very tiny, but they still form a liquid. Take, for example, hydrogen sulphide (H2S). Although sulphur is heavier atom than oxygen (and solid at normal conditions), H2S is a gas. The same goes for ammonia (NH3) and hydrogen chloride (HCl) which are both gases as well.

The mysterious thing that gives water the unique properties mentioned above is the hydrogen bond. It is a weak chemical bond that attracts the positively charged hydrogen atoms of one water molecule and the negatively charged oxygen atoms of the neighbouring water molecules. Oxygen possesses higher electronegativity than hydrogen, thus attracts the hydrogen electron which gives oxygen a partially negative charge. Consequently, the hydrogen atom then becomes partially positive. As you know, opposite charges attract each other and thus the molecules of water are closer together which results in water being liquid instead of a gas. The molecules of water are closest to each other at 4°C. As the temperature decreases further, the hydrogen bonds adjust to hold the negatively charged oxygen atoms a bit more apart with lots of tiny gaps. That explains the lower density of ice.

It’s like in relationships! The opposite personalities may form a stronger connection than two people who are similar. They kind of complete each other. Oxygen and hydrogen are light but if they combine their properties in one molecule and there is more of these molecules, something unusual forms, something surprisingly strong and that is water as we know it. Without this fascinating connection, the environment of Earth would not let the life evolve into such intelligent creatures like humans.

Wait, there is more! Way more! Not to overwhelm you with a flood of information, I am going to finish here. Tune in next week and continue our journey through unique properties of water!