Representing Ionic Bonding (Edexcel A Level Chemistry)

• Dot and cross diagrams are diagrams that show the arrangement of the outer-shell electrons in an ionic or covalent compound or element
  • The electrons are shown as dots and crosses

• In a dot and cross diagram:
  • Only the outer electrons are shown
  • The charge of the ion is spread evenly which is shown by using brackets
  • The charge on each ion is written at the top right-hand corner

Ionic compounds

• Ionic bonds are formed when metal atoms transfer electrons to a non-metal to form a positively charged and negatively charged ion
• The atoms achieve a noble gas configuration

 

Dot-and-cross diagrams of ionic compounds in which one of the atoms transfers their valence electrons to the other

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

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 (N^3-)
  • 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

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 (O^2-)
  • 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