Edexcel International AS Chemistry

Revision Notes

1.6.2 Ionic Bonding & Structures

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Ionic Dot-and-Cross Diagrams

  • As a general rule, metals are on the left of the periodic table and nonmetals are on the right-hand side
  • Ionic bonding involves the transfer of electrons from a metallic element to a non-metallic element
  • Transferring electrons usually leaves the metal and the non-metal with a full outer shell
  • Metals lose electrons from their valence shell forming positively charged cations
  • Non-metal atoms gain electrons forming negatively charged anions
  • Once the atoms become ions, their electronic configurations are the same as a noble gas
    • A potassium ion (K+) has the same electronic configuration as argon: [2,8,8]+
    • A chloride ion (Cl-) also has the same electronic configuration as argon: [2,8,8]-

Chemical Bonding Metals forming Cations, downloadable AS & A Level Chemistry revision notes

Forming cations by the removal of electrons from metals

Chemical Bonding Non-metals Forming Anions, downloadable AS & A Level Chemistry revision notes

Forming anions by the addition of electrons to nonmetals

  • Cations and anions are oppositely charged and therefore attracted to each other
  • Electrostatic attractions are formed between the oppositely charged ions to form ionic compounds
  • The ionic bond is the electrostatic attraction formed between the oppositely charged ions, which occurs in all directions ( this called non-directional bonding)
  • This form of attraction is very strong and requires a lot of energy to overcome
    • This causes high melting points in ionic compounds

 Chemical Bonding Forming Ionic Compounds, downloadable AS & A Level Chemistry revision notes

Cations and anions bond together using strong electrostatic forces, which require a lot of energy to overcome

  • The ions form a lattice structure which is an evenly distributed crystalline structure
  • Ions in a lattice are arranged in a regular repeating pattern so that positive charges cancel out negative charges
  • The attraction between the cations and anions is occurring in all directions
    • Each ion is attracted to all of the oppositely charged ions around it

  • Therefore the final lattice is overall electrically neutral
     Chemical Bonding Ionic Lattice, downloadable AS & A Level Chemistry revision notes

Ionic solids are arranged in lattice structures

Dot and cross diagrams 

  • These 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

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.