Ionic Bonds: Dot & Cross Diagrams (Edexcel IGCSE Chemistry: Double Science)

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Dot and cross diagrams for ionic compounds

  • Ionic bonds can be represented diagrammatically using dot-and-cross diagrams
    • The electrons from each atom should be represented by using solid dots and crosses
    • If there are more than two atoms, then hollow circles or other symbols / colours may be used to make it clear
    • The large square brackets should encompass each atom and the charge should be in superscript and on the right-hand side, outside the brackets

Sodium chloride dot and cross diagram

  • 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-
  • The formula of sodium chloride is NaCl

Dot and cross diagram for sodium chloride 

Ionic bonding – Sodium Chloride, IGCSE & GCSE Chemistry revision notesSodium loses one electron, and chlorine gains one electron. 

Magnesium oxide dot and cross diagram

  • 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-
  • The formula of magnesium oxide is MgO

Dot and cross diagram for magnesium oxide

Magnesium Oxide dot & cross diagram, IGCSE & GCSE Chemistry revision notes

Magnesium loses two electrons and oxygen gains two electrons. 

Examiner Tip

For exam purposes you need only show the outer electrons in dot & cross diagrams.

You should be able to draw dot & cross diagrams for combinations of ions from groups 1,2,3,5,6 and 7.

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Stewart

Author: Stewart

Expertise: Chemistry Lead

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Exam Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.