Ionic Bonding


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 called anions.

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.


Fill in these missing words ...

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.

You have had tries to get this right


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 eighteen electrons.

However, both ions now have eight electrons in their outer shell.

sodium and chlorine ions


Now answer these questions:

  1. How many electrons does a sodium atom have ?
  2. How many electrons does a chlorine atom have ?
  3. How many electrons does a sodium atom want to lose ?
  4. How many electrons does a chlorine atom want to gain ?
  5. How many electrons does a sodium ion have ?
  6. How many electrons does a chloride ion have ?
  7. What is a positive ion called ?
  8. What is a negative ion called ?
  9. How many electrons do atoms want to have in their outside shells ?
  10. What sort of ion is sodium ?

You scored out of 10 on that test