1.40: Draw Dot-and-Cross Diagrams to Show the Formation of Ionic Compounds by Electron Transfer, Limited to Combinations of Elements from Groups 1, 2, 3 and 5, 6, 7

IONIC COMPOUNDS: Formed when atoms of Metals transfer Electrons to atoms of Non-Metals to form Compounds made up of ions

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DOT-AND-CROSS DIAGRAMS: Shows the ionic bonds between ions formed from the loss and gain of Electrons

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• Only the outer shell of Electrons are drawn
• Electrons in one atom will be represented as Crosses, whilst Electrons in other atom will be represented as circles to indicate which ion loses or gains Electrons
• Charges of each ion is displayed on the upper right corner of each ion

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Example 1:

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Sodium Chloride, NaCl (typical ionic bond)

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Diagram showing the Dot-and-Cross Diagram of Magnesium Oxide

EXPLANATION Sodium is a Group 1 Metal so will lose one outer Electron to another atom to have a full outer shell of Electrons They will lose an Electron to form a Positive ion with the Charge 1+ Chlorine is a Group 7 Non-Metal so will 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 Chlorine atom will gain an Electron to form a Negative ion with Charge 1-           FORMULAE OF IONIC COMPOUND:    NaCl

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Example 2:

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Magnesium Oxide, MgO, is a Typical Ionic Bond

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Diagram Showing the Dot-and-Cross Diagram of Magnesium Oxide

EXPLANATION Magnesium is a Group 2 Metal so will lose two outer Electrons to another atom to have a full outer shell of Electrons They will lose two Electrons to form a Positive ion with the Charge 2+ Oxygen is a Group 6 Non - Metal so will 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-           FORMULAE OF IONIC COMPOUND:    MgO