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 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-

Groups 1&2 and 6&7 are the most likely to form ions

• 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

Examples of formation:

• 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-

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