Ions

In some compounds, electrons have been transferred from one atom to another.

This means that the atom will become:

• negatively charged if it has gained electrons and

• positively charged if it has lost electrons.

These particles are called ions.

Metals lose electrons and become positive ions.

Non-metals usually gain electrons and become negative ions.

When an atom becomes an ion it has the same electron arrangement as one of the group 0 elements (for example neon).

You will learn about this in much more detail at a later stage in chemistry.

Examples of Ions

A sodium ion has 11 protons, 12 neutrons and 10 electrons. Its electron arrangement is 2, 8. It can be written as follows:

A chloride ion has 17 protons, 18 neutrons and 18 electrons. Its electron arrangement is 2, 8, 8.

Notice that it is now called a chloride ion not a chlorine ion because it is part of a compound. It can be written as follows:

Next section: Isotopes