Representing Ionic Bonding (Edexcel AS Chemistry)

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Philippa

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Ionic Dot-and-Cross Diagrams

  • 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

 

Chemical Bonding Ionic Dot & Cross, downloadable AS & A Level Chemistry revision notes

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

Worked example

Draw a dot cross diagram for 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

Chemical Bonding Lithium Nitride Cross Diagram, downloadable AS & A Level Chemistry revision notes

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

Worked example

Draw a dot cross diagram for 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

Chemical Bonding Aluminium Oxide Cross Diagram, downloadable AS & A Level Chemistry revision notes

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

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Philippa

Author: Philippa

Expertise: Chemistry

Philippa has worked as a GCSE and A level chemistry teacher and tutor for over thirteen years. She studied chemistry and sport science at Loughborough University graduating in 2007 having also completed her PGCE in science. Throughout her time as a teacher she was incharge of a boarding house for five years and coached many teams in a variety of sports. When not producing resources with the chemistry team, Philippa enjoys being active outside with her young family and is a very keen gardener.