CIE A Level Chemistry复习笔记1.3.5 Ionic Bonding Examples

Sodium chloride

• Sodium is a Group 1 metal
  • It loses its outer electron to form a sodium ion with a +1 charge (Na⁺)
• Chlorine is a Group 7 non-metal
  • It gains 1 electron to form a chloride ion with a -1 charge (Cl^-)
• The oppositely charged ions are attracted to each other by electrostatic forces to form NaCl (ionic bonds)
• The final ionic solid is neutral in charge

Dot and cross diagram to show the ionic bonding in sodium chloride

Magnesium oxide

• Magnesium is a Group 2 metal
  • It loses its 2 outer electrons to form a magnesium ion with a +2 charge (Mg²⁺)
• Oxygen is a Group 6 non-metal
  • It gains 2 electrons to form an oxide ion with a -2 charge (O^2-)
• The oppositely charged ions are attracted to each other to by electrostatic forces to form MgO (ionic bonds)
• The final ionic solid is neutral in charge

Dot and cross diagram to show the ionic bonding in magnesium oxide

Calcium fluoride

• Calcium is a Group 2 metal
  • It loses its 2 outer electrons to form a calcium ion with a +2 charge (Ca²⁺)
• Fluorine is a Group 7 non-metal
  • It gains 1 electron to form a fluoride ion with a -1 charge (F^-)
• As before, the positive and negative ions are attracted to each other via an ionic bond
• However, to cancel out the 2+ charge of the calcium ion, 2 fluorine atoms are needed
  • Each fluorine atom can only accept 1 electron from the calcium atom
  • 2 fluoride ions will be formed
• Calcium fluoride is made when 1 calcium ion and 2 fluoride ions form ionic bonds, CaF₂
• The final ionic solid of CaF₂ is neutral in charge

Dot and cross diagram to show the ionic bonding in calcium fluoride

Worked example: Dot & cross lithium nitride

Answer

• Lithium is a Group 1 metal
• It loses its outer electron to form a lithium ion with a +1 charge (Li+)
• Nitrogen is a Group 5 non-metal
• It gains 3 electrons to form a nitride ion with a -3 charge (N3-)
• To cancel out the -3 charge of the nitride ion, 3 lithium atoms are needed and 3 lithium ions will be formed
• Lithium nitride is made when 1 nitride ion and 3 lithium ions form ionic bonds
• The final ionic solid of Li₃N is neutral in charge

Dot and cross diagram to show the ionic bonding in lithium nitride

Worked example: Dot & cross aluminium oxide

Answer

• Aluminium is a Group 3 metal
• It loses its outer electrons to form an aluminium ion with a +3 charge (Al3+)
• Oxygen is a Group 6 non-metal
• It gains 2 electrons to form an oxide ion with a -2 charge (O2-)
• To cancel out the negative and positive charges, 2 aluminium and 3 oxygen atoms are needed
• Aluminium oxide is made when 2 aluminium ions and 3 oxygen ions form ionic bonds
• The final ionic solid of Al₂O₃ is neutral in charge

Dot and cross diagram to show the ionic bonding in aluminium oxide