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• Ionic bonding


  The strong electrostatic force of attraction between oppositely charged ions formed by electron transfer
• Formation of ions


  1. Metal atoms lose electrons to form +ve ions

  2. Non-metal atoms gain electrons to form -ve ions
• Ionic bonding examples


  • Mg2+ 1s2 2s2 2p6
  • O2- 1s2 2s2 2p6
• Factors affecting ionic bonding strength


  • Smaller ions
  • Higher charges
• Ionic bonding examples


  • MgO has higher melting point than NaCl
• Ionic crystals


  Giant lattices of ions
• Ions with same electronic structure (of noble gas Ne)


  • N3-
  • O2-
  • F-
  • Na+
  • Mg2+
  • Al3+
• Factors affecting ionic radius


  • Increasing number of protons
  • Same number of electrons
• Ionic radius changes


  • Increases going down a group
  • Positive ions are smaller than atoms
  • Negative ions are larger than atoms
• 1. ray diffraction shows the likelihood of finding electrons in a region and the regular pattern of ions in NaCl
• Evidence for existence of ions


  • High melting points
  • Non-conductor of electricity when solid
  • Conductor of electricity when in solution or molten
  • Brittle / easy to cleave apart
• Covalent bonds are strong and caused by electrostatic attraction between bonding shared pair of electrons and nuclei
• High melting points of giant atomic structures like diamond and graphite demonstrate the strength of covalent bonds
• 1. ray diffraction shows high concentration of negative charge between H nuclei in H2
• In covalent compounds there is significant electron density between the atoms
• Effect of multiple bonds


  • Greater electron density between nuclei
  • Shorter bond length
  • Greater bond strength
• Dative covalent bond


  Shared pair of electrons comes from only one of the bonding atoms
• Examples of dative covalent bonds


  • NH4+
  • H3O+
  • NH3BF3
• Dative covalent bond acts like an ordinary covalent bond when thinking about shape
• Example of dative covalent bonding

  • Al2Cl6
• Carbon allotropes


  • Macromolecular structure with high melting points
  • Diamond has tetrahedral arrangement and cannot conduct electricity
  • Graphite has planar arrangement and can conduct electricity along layers
• Carbon nanotubes


  • High tensile strength
  • Can conduct electricity along the tube
• Graphene


  • High tensile strength
  • Can conduct electricity along the structure
• Electronegativity


  Relative tendency of an atom in a covalent bond to attract electrons
• Factors affecting electronegativity


  • Increases across a period
  • Decreases down a group
• Polar covalent bond


  Bond with unequal distribution of electrons, producing a charge separation (dipole)
• Symmetric molecules with identical bonds and no lone pairs are non-polar
• Ionic and covalent bonding are extremes of a continuum, with intermediate bonding possible
• Charged rod experiment shows effect of polarity on liquid jet deflection
• Polar molecule


  Molecule with an uneven distribution of electrons, resulting in a net dipole moment
• Non-polar molecule


  Molecule with a symmetrical shape and no net dipole moment
• CO2 is a symmetrical molecule and is a non-polar molecule
• Electronegativity


  Measure of the ability of an atom to attract shared electrons in a covalent bond, on the Pauling scale from 0 to 4

  
• The most electronegative element is fluorine and it is given a value of 4.0
• Ionic bonding


  Bonding between oppositely charged ions
• Covalent bonding


  Bonding by the sharing of electrons between atoms
• Ionic and covalent bonding are the extremes of a continuum of bonding type
• Differences in electronegativity between elements can determine where a compound lies on the ionic-covalent bonding continuum

  
• In this experiment, a charged rod (formed by rubbing a plastic rod) is brought close to a jet of liquid flowing from a burette
• If the liquid is polar


  The jet of liquid will be attracted to the electrostatic force of the rod