Ionic Bonds: Dot & Cross Diagrams (Edexcel IGCSE Science (Double Award) (Modular)): Revision Note

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 

Sodium 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 loses two electrons and oxygen gains two electrons.