What is an atom?

Everything is made up of tiny building blocks, known as atoms.

Atoms are so small that they cannot be seen by even the most powerful optical microscope. To see atoms, scientists must use a special type of microscope known as a scanning tunnelling microscope or STM.

There are 118 known types of atoms and only 91 of these are found naturally on Earth. The rest can only be made in a lab.

Inside an Atom

Scientists once thought that atoms were hard and unbreakable. Today, they know that atoms are made up of even smaller particles known as subatomic particles.

Each atom is made up of three types of subatomic particles: protons, neutrons and electrons.

The Nucleus

Protons and neutrons form a cluster that sits at the centre of the atom. This cluster is known as the nucleus.

Protons have a positive charge and neutrons have a neutral charge (this means they are not negative or positive).

Electrons

Electrons are much smaller and move very fast around the nucleus in layers called shells. There are usually the same number of electrons as protons.

Electrons have a negative charge.

​An electron is 1/1840 of the size of a proton or neutron.

Have a think...

In your table groups, observe what happens when you hold the same ends together and then opposite ends. Use what you saw to explain:

• ​Why do atoms need neutrons in the nucleus?

• Why don’t electrons get pulled into the nucleus, even though their charge is opposite to protons?

Write these questions and your answers into your books.