What Makes Water the Most Important Molecule in the Universe?

In this blog, we dive deep into the world of water, exploring its covalent and hydrogen bonding, the remarkable qualities of cohesion and adhesion, its inherent polarity, and how these factors make it essential for life on Earth. Join me on a journey to understand why water is more than just a simple molecule; it's the foundation of existence.

Image Source - Cup of water on the table

Picture this: It's a hot summer day and you're relaxing on the lake. Everyone is enjoying themselves in the water, splashing the clear fluid up into the air. You've been running on the beach all day and finally sit down with sweat dripping down your face. You hear a sharp slap and look at the docks where a child has just belly flopped while cliff jumping. You look at the drink in your hand and notice the water clinging to the sides of the straw.

There are many unique properties of water that can make this happen. Let's break them down into the fundamental ideas.


What makes all of these things happen?

Water is an extremely complex molecule with many reasons as to why things happen. Let's start at the beginning, zooming in to the molecule and understanding exactly what it's made of.

What is water?

Water consists of two different elements. Hydrogen (H) and Oxygen (O); many times, you will see water written as H2O — which is the chemical formula for the molecule — and this tells us that water is made up of 2 hydrogen atoms and one oxygen atom.

Covalent Bonds

These atoms are bonded through covalent bonds which is nothing but the linkage of atoms through shared electrons. The sharing of electrons within the water molecule isn't equal however and this is due to the difference in sizes of the two atoms. With Oxygen containing 8 protons (compared to Hydrogen's 1) it has a much larger positive charge. Opposites will always attract in nature and so, the negative electron of the Hydrogen is slightly drawn to the large postive charge of the Oxygen.

This unbalance of charge gives Oxygen a slightly negative charge and Hydrogen a slightly positive charge. This is known as polarization and it is the source of water's unique properties.

Polarization

Polarization, like all things in nature, is binary; it can either be polar or non-polar. A polar molecule is any molecule that has an unequal sharing of charge, water being a perfect example of this. Non-polar molecules are molecules with an equal share of charge such as carbon dioxide (CO2).

This also means that polar molecules and non-polar molecules don't interact together. In fact, they repel each other. Have you ever seen oil sitting on top of water? No matter how much you stir it, the two will never mix and due to oil's lesser density, it will sit right on top of the water molecules.

Why do we belly flop?

Why is it that when we pencil dive into a pool, the water separates at our feet and we just disappear under the surface but when we belly flop, the water turns to concrete and it stings?

Hydrogen Bonding

Hydrogen bonding is another type of bonding which links two molecules together. Due to the polarization of water, oxygen has a slight negative charge and Hydrogen has a slight positive charge. This leads to further attraction between the positive Hydrogen end of a water molecule and the negative Oxygen end of another water molecule.

Hydrogen bonds also have great heat absorption capabilities. This is known as specific heat, or the amount of energy it takes for 1 gram of an object to heat up 1°C.
For example, the specific heat of aluminum is 0.900 joules per gram in celsius (J/g C) whereas the specific heat of water is 4.186 J/g C. Notice how it takes much more (a little more than 4.5 times!) energy to heat up water than aluminum?

Cohesion

The sticking together of two like substances is called cohesion. Due to the hydrogen bonds, water molecules like to stick together, strenthening the amount of force needed to break those bonds. This phenomenon is called surface tension. This is what allows for water droplets to form a dome shape when on a penny or on a wall.

Adhesion

Wait...how do water droplets stick to walls? This is due to adhesion which is the ability of a substance to stick to other things. This means that not only is water attracted to its own charged ends, but its also attracted to other polar molecules (or other molecules with charged ends).

How can we apply this to the real world?

Let's picture the day at the lake again. Now that we know about water, let's look at a few of the ordinary things that happened that day in a new perspective.

Sweating

That hot day lead to you breaking out into a sweat. This is your body's way of cooling down. The sweat absorbs the heat from your body due to the hydrogen bonds within the water molecules that your sweat contains. In fact, water is the primary way that your body regulates its temperature. By moving water from different areas in your body, we are able to absorb and transfer heat due to that great specific heat.

The belly flop

In physics, force is inversely proportional to area. This is because the greater the force is, the less force must be applied per square meter (m2) A good example of this is a hammer and a knife. When cutting something, a hammer simply cannot do it. Have you ever seen a hammer pierce wood (piercing is different from breaking)? A knife of the other hand can pierce almost anything perfectly. This force-area proportionality is the reason. The hammer applies the force over a greater area which weakens the force while the knife projects all the force to a certain point amplifying the force.

This proportionality exists in the problem of the belly flop. The cohesion of the water, through hydrogen bonds, creates surface tension. When we pencil dive, all of our gravitaional force is projected to a small area: our toes. When we belly flop, our gravitational force is distributed throughout our entire body, reducing the force per square meter.

Due to the reduced force in our belly flop, the hydrogen bonds don't break and we hit the surface of the water as opposed to going through it.

Water clinging to the straw

This is a perfect example of adhesion! The water molecules are attracted to a substance that makes up the straw (it doesn't matter what that substance is. As long as it has a slight charge, water will cling to it). In fact, this is what allows trees to move water up and down their trunks! The water's cohesion helps keep water molecules together and the adhesion of water to the inner tube of the tree allow for water to move upwards and evaporate out of the top of the tree!

Why is water so important?

Whenever astonomers search for interstellar life, they are searching for water.

Water is vital for organisms to alive. With it being a powerful solvent, it allows for vital chemical reactions and it helps regulate body temperature among organisms.

Hopefully now that you know a little bit more about water, the next time you take a sip, you'll think back to how water allows for life to exist on our planet and how it is the most important molecule in the universe.

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