Gaining and Losing Electrons

The diagram below shows a beryllium atom on the left and a beryllium ion on the right. They both have 4 protons and they both have 5 neutrons. In other words, their nuclei are identical. The only difference between them is the amount of electrons they have. The beryllium atom has 4 electrons, whereas the beryllium ion has 2 electrons.

A beryllium atom and a beryllium ion.

Atoms and ions can gain and lose electrons. In fact, this happens in many chemical reactions. We can see that if the beryllium atom lost 2 electrons it would become the beryllium ion. Similarly, if the beryllium ion gained 2 electrons it would become the beryllium atom.

A beryllium atom can become a beryllium ion by losing 2 electrons. A beryllium ion can become a beryllium atom by gaining 2 electrons.

What this means is that atoms can become ions and ions can become atoms. They can do this by gaining or losing electrons.

Atoms can become anions or cations

The type of ion that an atom becomes depends on whether it gains or loses electrons. If an atom gains electrons it will become a negatively charged ion (an anion). This is because it will have more electrons than protons. If it loses electrons it will become a positively charged ion (a cation). This is because it will have more protons than electrons.

Anions become atoms by losing electrons

An anion can become an atom by losing electrons. To begin with, it has more electrons than protons. Therefore if it loses enough electrons that its number of electrons equals its number of protons, it will become an atom.

Cations become atoms by gaining electrons

A cation can become an atom by gaining electrons. To begin with, it has more protons than electrons, so if it gains enough electrons that its number of electrons equals its number of protons, it will become an atom.

Ions can become other ions

As well as being able to turn into atoms, ions can also turn into other ions of the same element by gaining or losing electrons. For example, a copper ion with a relative charge of +2 (known as a Cu²⁺ ion) can turn into a copper ion with a relative charge of +1 (known as a Cu⁺ ion) by gaining an electron, and a Cu⁺ ion can turn into a Cu²⁺ ion by losing an electron:

A Cu+ ion can become a Cu2+ ion by losing an electron. A Cu2+ ion can become a Cu+ ion by gaining an electron.

The element does not change

When an atom gains or loses electrons, it can only ever turn into an ion of the same element as itself. Similarly, an ion can only ever turn into an atom or ion of the same element as itself.

For example, a magnesium atom can turn into a magnesium ion and a magnesium ion can turn into a magnesium atom or a different kind of magnesium ion, but a magnesium atom or ion could never turn into a sodium atom or ion by gaining or losing electrons.

This is because gaining or losing electrons does not affect the number of protons, which is what determines which element something is.

Flashcards

Flashcards help you memorise information quickly. Copy each question onto its own flashcard and then write the answer on the other side. Testing yourself on these regularly will enable you to learn much more quickly than just reading and making notes.