3. Theoretical and exterminator lattice enthalpies

• What affects strength of an Enthalpy of lattice formation ?

  • Size of ions
  • Charges of ions
• How does size of ions affect strength of enthalpy lattice formation?

  the larger the ions, the less negative the enthalpies of lattice formation. As the ions are larger the chargers become further apart and so have a weaker attractive force between them
• How does charge of ion affect strength of enthalpy of lattice formation?

  The bigger the charge of the ions charge, the greater the attraction between the ions so the stronger the lattice enthalpy ( more negative values )
• The lattice enthalpies become …… negative down any group


  Less
• How can theoretical lattice enthalpies be calculated from ?

  Data assuming a perfect ionic model
• What is the perfect ionic model?

  • Ions are 100% ionic
  • Ions are perfectly spherical
  • Attractions are purely electrostatic
• how can we identify a covalent character ?

  • Positive ion is small
  • The positive ion has multiple charges
  • The negative ion is large
  • The negative ion has multiple charges
• why does the experimental value differ from the theoretical value of lattice enthalpies ?

  Tells us the compound being experimented on doesn’t follow the perfectly ionic model and has some covalent characters
• What happens in a compound that contains some covalent character ?

  Most of the time the positive charge distorts the distribution in the negative negative ion. We say the positive ion polarise the negative ion

  
• What happens when the positive ion polarises the negative ion more ?

  The more polarisation we get, the more covalent character there will be