The Magic of Water - Part 1

© 2026 Kieron Conway - All rights reserved.

Water - The Astonishing Liquid

Water is something we all take for granted, but in fact it is the most astonishing liquid. Without it, none of us would be here, for reasons far beyond simply needing to drink it, as you'll see.

Its physical properties make it quite unique and totally fascinating. Many of the things it can do, chemistry tells us it shouldn’t be able to do! To understand what it does, you have to delve into the physics of how the enigmatic H₂O molecule behaves.

To start with: water freezes at 0°C and boils at 100°C. Yet chemistry suggests that it should be a gas at room temperature and boil at around –70°C.

How could chemistry get it so wrong?

Why Does Chemistry Say Water Should Be a Gas?

A single water molecule consists of one oxygen atom tightly bound to two hydrogen atoms. Oxygen is the lightest element in Group 16 of the periodic table. Below it are sulphur (S), selenium (Se) and tellurium (Te).

All these elements bond with two hydrogen atoms, giving us:

• H₂O (water)

• H₂S (hydrogen sulphide)

• H₂Se (hydrogen selenide)

• H₂Te (hydrogen telluride)

  
  

Here are their boiling points (from heaviest to lightest):

• H₂Te: 2°C to 4°C

• H₂Se: –41.25°C to –42.25°C

• H₂S: –60°C

• H₂O: +100°C ?

  
  

As you move down the list, the compounds become lighter and the boiling point decreases.

So, why on earth does H₂O, the lightest of the group, have a staggering boiling point of +100°C instead of about minus 70°C, as the trend would suggest?

PROPERTY 1 – Water’s High Boiling Point

Chemistry predicts a boiling point of about –70°C for water, meaning it should be a gas at room temperature.

The reason it isn’t? Hydrogen bonding and oxygen’s strong affinity for electrons.

More will be revealed as we delve deeper.

What Happens When Water Freezes?

If you drop a solid lump of H₂S into liquid H₂S, it sinks. The same happens with the other Group 16 hydrides: the solid sinks in its own liquid.

But solid water, more commonly called “ice” floats.

In fact, almost every substance becomes denser as it freezes. Water does the opposite.

As liquids get colder, they usually become more dense. Water does too, until it reaches 4°C. At this temperature, water reaches its maximum density. Below 4°C, it begins to expand.

By the time it freezes at 0°C, the solid ice is less dense than the liquid water, so it floats.

Water actually starts expanding below 4°C. That’s why frozen pipes crack, the expanding ice has nowhere to go.

PROPERTY 2 – Water Expands Below 4°C

Water reaches maximum density at 4°C and then becomes less dense as it cools further.

H₂O is not the only substance that expands near its freezing point, but it is by far the most important and familiar substance to perform this trick.

Again, this behaviour is due to hydrogen bonding and oxygen’s affinity for electrons.

Ice Is a Poor Conductor of Heat

Imagine a pond or lake during a cold winter. The air temperature drops well below 0°C and ice forms on the surface.

The ice does not sink, it thickens and forms a protective lid over the water. Because ice is a poor conductor of heat, the water beneath remains at around a balmy 4°C.

Even during long periods of freezing weather, fish and other aquatic life survive beneath the insulating ice layer.

PROPERTY 3 – Water Is a Poor Conductor of Heat

This characteristic has protected aquatic life for millions of years during cold periods, throughout evolution.

However, rather than defying the laws of thermodynamics, this behaviour is fully consistent with them. The hydrogen-bonded structure of ice simply slows the transfer of thermal energy.

Why Does It Take So Long to Boil Water?

Water has an enormous specific heat capacity: it can absorb large amounts of energy before its temperature rises significantly.

So, where is the energy from your kettle going? Much of it is being used to disrupt hydrogen bonds between water molecules before the molecules can move faster and increase in temperature.

PROPERTY 4 – Water Has a High Thermal Capacity

Water absorbs large amounts of heat energy before its temperature rises. This property helps moderate Earth’s climate and stabilise living organisms.

Again, hydrogen bonding is responsible.

How Can Insects Walk on Water?

You’ve probably seen insects walking across water without breaking the surface. You can even place a metal needle carefully on water and it may float.

This happens because water has very high surface tension, second only to mercury among common liquids.

High surface tension creates a “skin-like” surface that insects can stand on.

Surface tension also creates a meniscus in a glass of water, where the water climbs slightly up the sides of the glass.

In very thin glass tubes (capillary tubes), water can rise significantly above the surrounding level. This same capillary action helps giant redwood trees (some over 90 metres tall) draw water from their roots up to their leaves.

PROPERTY 5 – Surface Tension Effects

The surface molecules of water behave as though they form a stretched membrane, preventing small objects such as insects from breaking through.

Water molecules can link together through hydrogen bonds, forming chains that enable capillary action, along with adhesion and cohesion.

Surface tension allows water droplets to form, essential to the process of forming rain.

How Come So Many Things Dissolve In Water?

Water is an excellent solvent. It is usually the first substance we try to remove a stain.

It dissolves ionic compounds such as table salt (sodium chloride) extremely well. Water molecules surround the sodium and chloride ions and pull them into solution.

This solvent property is vital for life. Our bodies contain large amounts of water, and water provides the medium in which biochemical reactions occur throughout the body.

PROPERTY 6 – Water Acts as a Universal Solvent

Water dissolves a vast range of substances.

How? Stay tuned.

Water Is the Reason We Are Here

The six properties described above are central to life on Earth:

1. Water freezes at 0°C and boils at 100°C.

2. Water expands below 4°C and ice floats.

3. Water is a poor conductor of heat.

4. Water has a high thermal capacity.

5. Water has remarkable surface tension.

6. Water is an excellent solvent.

If ice didn't float, there would be no protection for aquatic life forms. Lakes and oceans would freeze from the bottom up and early forms of life would have struggled to survive winter.

Because water has a high thermal capacity, it moderates Earth’s climate.

Organisms made largely of water maintain stable internal temperatures. Sweating cools us efficiently because evaporation removes heat from the body.

Water can climb up the tallest trees under capillary action, from the roots to the leaves and evaporation from the leaves pulls more molecules up. No pumps are involved, just the magic of water at work. If water didn't do this, trees would be just several metres in height as a maximum.

Surface tension supports insects that become food for fish. Water’s solvent properties have allowed oceans to accumulate salts and enabled complex chemistry necessary for life.

It is almost as if water has been optimised by nature to support the development of life, both internally and externally, from single cell structures to humans.

Is There a Single Reason Water Is So Versatile?

It all comes down to hydrogen bonding.

Hydrogen consists of one proton and one electron. In a water molecule, two hydrogen atoms form covalent bonds with oxygen by sharing electrons.These covalent bonds give water its strength and its bent (boomerang-like) shape as depicted in the following image.

Because oxygen attracts electrons more strongly than hydrogen, the molecule has an uneven charge distribution. The oxygen end has a slight negative charge, and the hydrogen end has a slight positive charge.

This creates a dipole and allows hydrogen bonds to form between water molecules.

The resultant distribution of the water molecule's electron clouds is where the real magic begins.

Look out for part 2 of the Magic of Water, to read about the amazing physics of the water molecule.

Liked this article? Check out:

modern-physics-journey.com 

where you can read all about an exciting new science series: A Journey into Modern Physics, available from Amazon and Rakuten Kobo on-line shops.