Formation of Ions

• Ions are made when electrons are transferred
• Ions are charged particles - they can be single atoms or groups of atoms
• When atoms lose or gain electrons to form ions, all they're trying to do is get a full outer shell like a noble gas (also called a 'stable electronic structure')
• Atoms with full outer shells 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+
• Groups 1&2 and 6&7 are most likely to form ions
• The elements that mostly readily form ions are those in groups 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. They gain electrons to form negative ions (anions)
• Elements in the smae 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 they form ions with the same charges
• A sodium atom (Na) is in group 1 so it loses 1 electron to form a sodium ion (Na+) with the same electronic structure as neon:

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