Atoms

What are atoms?

Over 2000 years ago a Greek philosopher called Democritus suggested that everything was made up of tiny pieces. Democritus suggested that, if you would keep on cutting up a substance into smaller and smaller pieces, you would eventually end up with a very small piece that could not be cut up any more.

Democritus called his tiny pieces of matter atoms. ‘Atom’ means ‘cannot be divided’.

Carbon atoms seen with a scanning tunnelling microscope. Each little round bump is a single carbon atom. The photograph is magnified millions of times.

We now know that atoms really do exist. Today, we can we can even see some larger kinds of atoms, using very special microscopes called scanning tunneling microscope. The photograph shows the atoms in some carbon nanotubes. (‘Nano’ means very, very small.)

Different kinds of atoms

There are many different types of atoms. Scientists have discovered 94 different kinds of atoms that occur naturally in the Universe. Another 24 kinds of atoms have been made in laboratories.

Some substances are made up of just a single kind of atom. A substance that is made of just one kind of atom is called an element.

For example, carbon is made only of carbon atoms. Gold is made only of gold atoms. Silver is made of only silver atoms. Carbon, gold and silver are example of elements.

Each type of atom has different properties. This is why different elements have different properties.

Atoms joining together

Some substances are made up of individual atoms. For example, a piece of gold is made up of millions of individual gold atoms. Neon-which is a gas-is made up of individual neon atoms.

Other substances are made up of little groups of atoms. The atoms join together in groups of two or more.

A group of atoms joined tightly together is called a molecule.

Molecules of oxygen

Some elements are made up of molecules. For example, in oxygen the atoms are joined together in pairs. A molecule of oxygen is made from two atoms of oxygen joined together.

This sulfur molecule is made of eight sulfur atoms.

Sulfur molecules are made up of eight sulfur atoms joined together. They can be joined in slightly different ways.