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 could keep on cutting up a substance into smaller and smaller pieces, you would 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’.

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

Different types of atom

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

Some substances are made up of just a single kind of atom. A substance 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 only of silver atoms.
Carbon, gold and silver are examples of elements.

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

 

 

Atoms joining together

In six of the elements, such as neon (which is a gas), atoms move around freely, not attached to one another. But in most elements, such as gold and other metals, atoms are packed closely together.

In a small number of elements, such as oxygen and sulfur, atoms join together to form small particles. An oxygen particle is made from two oxygen atoms. A sulfur particle is made from eight sulfur atoms.

 

 

 

 

Arranging the elements

Scientists have developed a very useful way of arranging the elements. This is called the Periodic Table.

The full Periodic Table containing all of the 118 known elements is very large and complex. (There may be one on the wall of your science laboratory.) You are just going to look at the first 20 elements.

Groups and periods

The Periodic Table is organised into rows and columns. The rows are called periods. The columns are called groups.

The atoms are organised so that, as you read across each row (period) from left to right, the atoms increase in mass. Hydrogen atoms have the smallest mass, then helium atoms, then lithium atoms, and so on.

Chemical symbols

Each of the elements has been given a symbol. This is a useful shorthand way of referring to them.

• Sometimes the symbol is the first letter of the English name of the element. For example, the symbol for oxygen is O.
• Sometimes the symbol is the first letter of the English name plus another letter from its name. For example, the symbol for helium is He.
• Sometimes the symbol is taken from another language. For example, the symbol for sodium is Na, from the old Latin name ‘natrium’.

The first letter of the symbol is always upper case, and the second letter, if there is one, is always lower case.

Metals and non-metals

The Periodic Table is organised so that elements with similar properties are close together.

In the diagram of the Periodic Table, all the elements that are metals are in yellow boxes. All the elements that are non-metals are in blue boxes.