What is water made of? Atoms & Properties of a Water Molecule

Life on our planet wouldn’t have gotten very far without water. Its unique chemical properties allows it to stick together easily and dissolve other substances—crucial behaviours that made it usable by animals and plants, which quickly evolved and exploded across the planet.
But what is water made of, exactly? And why does it behave in this way?

Water is made of two hydrogen atoms and one oxygen atom that are bonded together. That’s why it’s called H2O. The H2 is for the two hydrogen atoms, and the O is for the single oxygen atom.

Because water is a group of different atoms bonded together, it’s called a molecule. It forms a (upside down) V-shape, as shown in the image below:

A water molecule is just 0.27 nanometers wide, and a single drop of water contains about 150,000,000,000,000,000,000 of them. That’s a lot of molecules. Imagine how many you use in the shower in the morning!

The hydrogen and oxygen atoms in a water molecule are stuck together with something called a covalent bond. This is a type of strong connection where atoms share one or more pairs of electrons, but the interesting thing about water is its unique electromagnetic charge, and is the reason for its incredibly useful properties.

The atoms in oxygen are electronegative, and therefore attract the electrons in their shared bond with the two hydrogen atoms. This makes the entire molecule polar, with negative charges on the oxygen’s side, and positive charges on the hydrogen’s side. Because of this polarity, the two opposite charges attract one another, which creates a weak charge called a hydrogen bond, and is the reason that water is a liquid at room temperature. The unfathomable number of hydrogen bonds that are found in a drop of water cause the molecules to hold together for tiny fractions of a second, which creates the liquid substance you know as water. When they are heated to 100°C, they become steam and try to disperse, but the hydrogen bonds slows down this process by pulling them back together again, and as they cool, they condense and turn back into water. Because water molecules are always trying to stick together in this way, they can form larger bodies of water which can be accessed by plants and animals.

As if this wasn’t useful enough, the polarity and abundance of water molecules also means that they are easily attracted to other molecules, which they surround, carry to other places, and dissolve. This makes them the “universal solvent” that allows them to transport chemicals, minerals, and nutrients around the bodies of animals and plants, where they can be used to support the organism.
That’s what water is made of in a nutshell. But what about its atoms, hydrogen and oxygen?

Hydrogen is a chemical element with the symbol H. It’s the lightest element that we know of, and the most abundant in the universe, making up about 75% of matter.1 Its colourless, odourless, and tasteless, and is present in nearly all living things. The name “hydrogen” comes from the Greek word “hydro” and “genes”, which mean “water forming.”

Oxygen has the chemical symbol O. It’s the Earths’ most abundant element, and the third most abundant element in the universe. Its name is also derived from two Greek words: “oxy” and “genes,” which mean “acid forming.”

Water is originally believed to have come from water-rich minerals that melted when the planet was forming, as well as icy comets that smashed into the Earth. The total volume of water on Earth always stays the same because making water is extremely difficult and expensive. Until we’re hit by another icy comet, or have advanced technology to the point of being able to create new water molecules, we always have a limited, precious supply. Some of the water molecules you drank today may have once been in the gut of William Shakespeare or Steve Irwin. Lucky you!

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