Formation of Ions

Ions are charged particles-they can be single atoms or groups of atoms
When atoms lose of gain electrons to form ions, all they’re trying to do is get a full outer shell like a noble gas
- Atoms with full outer shell are very stable
When metals form ions, they lose electrons from their outer shell to form positive ions
When non-metals form ions, they gain electrons into their outer shell to form negative ions
The number of electrons lost or gained is the same as the charge on the ion
- E.g. If 2 electrons are lost the charge is 2+.
- If 3 electrons are gained the charge is 3-

The elements that most readily form ions are those in Group 1,2,6 and 7
Group 1 and 2 elements are metals and they lose electrons to form positive ions(cations)
Group 6 and 7 elements are non-metals and they gain electrons to form negative ions(anions)
You don’t have to remember what ions most elements form
- You just look at the periodic table
Elements in the same group all have the same number of outer electrons
So they have to lose or gain the same number to get a full outer shell
- This means that they form ions with the same charges
Group 1 elements form 1+ ions
Group 2 elements form 2+ ions
Group 6 elements form 2- ions
Group 7 elements form 1- ions

A sodium atom is in Group 1 so it loses 1 electron to form a sodium ion with the same electronic structure as a neon
- Na-Na+ + e-
A magnesium atom is in Group 2 so it loses 2 electrons to form a magnesium ion with the same electronic structure as neon
- Mg-Mg2+ + 2e-
A chlorine atom is in Group 7 so it gains 1 electron to form a chloride ion with the same electronic structure as argon
- Cl + e- - cl-
An oxygen atom is in Group 6 so it gains 2 electrons to form an oxide ion with the same electronic structure as neon
- O + 2e- - O2-