Home : Structures : Ionic Bonds
a sodium atom
a chlorine atom
In lesson 11 we saw that when atoms either lose electrons or gain extra
electrons they are called ions. Atoms that lose an electron are called cations ... and atoms that gain an electron are
If you look at the diagrams of the sodium and chlorine atoms you can see that sodium normally has eleven electrons in shells around the
nucleus. You can also see that chlorine has seventeen electrons around its nucleus. Both of these atoms would be happier if they had eight
electrons in their outside shells.
The easiest way for sodium to do this is for it to lose an electron - and chlorine can do this by gaining
an extra electron.
When atoms lose or gain electrons they are called . If an atom gains an it is
called an anion. When an atom loses an electron it is called a .
A sodium atom has eleven and a atom has seventeen electrons.
The sodium atom and the chlorine atom want to make their outside shells contain
only eight electrons. The sodium atom wants to lose an electron and the chlorine atom wants to gain an electron.
When the two atoms come together the electron from the sodium atom jumps into the gap in the outer shell of the chlorine atom.
If you look at the diagram the sodium ion (a cation) now contains only ten electrons and the new chloride ion (an anion) has
However, both ions now have eight electrons in their outer shell.