CIE IGCSE Chemistry

Revision Notes

3.2 Ions & Ionic Bonds

The Formation of Ions


  • An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons
  • This loss or gain of electrons takes place to gain a full outer shell of electrons
  • The electronic structure of an ion will be the same as that of a noble gas – such as helium, neon and argon


Formation of positively charged Sodium ion1Formation of  positively charged sodium ion



Formation-of-negatively-charged-Chloride-ion1, IGCSE & GCSE Chemistry revision notesFormation of  negatively charged chloride ion


Ionisation of metals and non-metals

  • Metals: all metals lose electrons to other atoms to become positively charged ions
  • Non-metals: all non-metals gain electrons from other atoms to become negatively charged ions

Electrostatic attraction

  • The positive and negative charges are held together by the strong electrostatic forces of attraction between opposite
  • This is what holds ionic compounds together


Oppositely charged ions attraction due to electrostatic attraction, IGCSE & GCSE Chemistry revision notes Electrostatic forces between the positive Na ion and negative Cl ion

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Ionic Bonds between Metallic & Non-Metallic Elements

Example:  Sodium Chloride, NaCl

Ionic bonding – Sodium Chloride, IGCSE & GCSE Chemistry revision notesSodium chloride ionic bonding



  • Sodium is a group 1 metal so will lose one outer electron to another atom to gain a full outer shell of electrons.
  • A positive sodium ion with the charge +1 is formed.
  • Chlorine is a group 7 non-metal so will need to gain an electron to have a full outer shell of electrons.
  • One electron will be transferred from the outer shell of the sodium atom to the outer shell of the chlorine atom.
  • A chlorine atom will gain an electron to form a negatively charged chloride ion with a charge of -1.

Formula of ionic compound:    NaCl


Example:  Magnesium Oxide, MgO

Magnesium Oxide dot & cross diagram, IGCSE & GCSE Chemistry revision notesDiagram showing the dot-and-cross diagram of magnesium oxide



  • Magnesium is a group 2 metal so will lose two outer electrons to another atom to have a full outer shell of electrons
  • A positive ion with the charge +2 is formed
  • Oxygen is a group 6 non-metal so will need to gain two electrons to have a full outer shell of electrons
  • Two electrons will be transferred from the outer shell of the magnesium atom to the outer shell of the oxygen atom
  • Oxygen atom will gain two electrons to form a negative ion with charge -2

Formula of ionic compound:    MgO

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The Lattice Structure of Ionic Compounds

Lattice structure

  • Lattice structure refers to the arrangement of the atoms of a substance in 3D space
  • In lattice structures, the atoms are arranged in an ordered and repeating
  • The lattices formed by ionic compounds consist of a regular arrangement of alternating positive and negative ions


NaCl 3-D Structure, IGCSE & GCSE Chemistry revision notesThe lattice structure of NaCl

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.

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