What Are Atoms? The Essential Building Blocks of All Matter

Atoms are the smallest units of chemical elements that retain the chemical properties of those elements.

They are the basic building blocks of everything that can be seen or touched, including me, you and every other living thing on our planet.

Apart from a hydrogen atom, which has just one proton and one electron, other types of atoms are made up of different numbers of protons, neutrons and electrons.

A chemical element is a pure substance made of atoms that have the same number of protons in their nucleus, and the number of protons is known as the atomic number.

The mass number of an atom is the total number of protons and neutrons combined. To give you an idea of the size of an atom and how small they are, take a human being of, say, 70 kilograms (154 pounds) in weight. The total number of atoms making up that person's body is estimated to be about 7 octillion, which is a staggering 7,000,000,000,000,000,000,000,000,000 atoms!

During our lives, vast numbers of atoms keep joining and leaving our bodies. Every breath we take, every meal we eat and every drink we have introduces new atoms into our bodies, while other atoms leave through breathing, perspiration and other natural bodily processes.

The most abundant elements by mass that make up about 99% of the human body are oxygen, carbon and hydrogen.

When we die, all the elements we were made of will gradually return to the environment, eventually becoming part of other objects or even other living things in the future.

Under ordinary chemical conditions, atoms cannot be destroyed; they are simply rearranged into different substances and continue to be recycled throughout nature.

A molecule is an electrically neutral group of two or more atoms held together by chemical bonds; they can be simple or complex. To give an example, a water molecule consists of one oxygen atom and two hydrogen atoms bonded together.

A carbon dioxide molecule has one carbon atom and two oxygen atoms bonded together. Some molecules contain only a few atoms, while others, such as proteins and DNA, contain thousands or even millions.

Matter is the term used for anything that has mass and takes up space. It is all around us. Matter is the air you breathe, the shoes you wear, the water in your glass and everything you can touch. It is what we are.

The three most commonly known states of matter are solid, liquid and gas. The difference between these states depends on how closely packed the particles are and how freely they are able to move. A solid has tightly packed particles, a liquid has particles that can move past one another, and a gas has particles that move freely in all directions.

It took roughly 380,000 years after the birth of the Universe for electrons to become bound to atomic nuclei, thus forming the first atoms. These first atoms were mainly hydrogen and helium, with tiny amounts of lithium. Hydrogen is still the most abundant element in the universe today.

As I said, a simple hydrogen atom contains just one proton at its centre and one electron. You could say that atoms are mostly empty space. Although electrons are often shown orbiting the nucleus like planets around the Sun, they actually exist in regions of probability called orbitals, where they are most likely to be found.

To give an idea of how far the electron could be from the nucleus of a hydrogen atom, imagine this: scale the proton up to the size of a golf ball.

At that scale, the electron could be as far as 2 kilometres (1.2 miles) from the centre of the atom, giving the atom a diameter of roughly 4 kilometres (2.5 miles). This comparison helps to illustrate just how much of an atom consists of empty space.

An atom can be about 0.1 to 0.5 nanometres in diameter. There are 1,000,000,000 nanometres in one metre. Yes, atoms are extremely small, yet they are the fundamental building blocks from which everything around us is made.

British spelling!

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