13A: Lattice energy Flashcards
Use PPQs for spec points: 3, 10
Define lattice energy
The energy change when
- 1 mole of an ionic solid is formed
- from its gaseous ions
Define enthalpy change of atomisation
The enthalpy change when
- 1 mole of gaseous atoms is formed
- from its elements in their standard states
Define first electron affinity
The enthalpy change when
- 1 mole of gaseous atoms
- gains 1 mole of electrons to form 1 mole of gaseous -1 ions
Define second electron affinity
The enthalpy change when
- 1 mole of gaseous -1 ions
- gains 1 mole of electrons
- to form 1 mole of gaseous -2 ions
State which energy value provides a measure of ionic bond srength.
Lattice energy
State what a comparison of the experimental lattice energy value with the theoretical value would indicate.
The degree of covalent bonding
Describe polarisation as applied to ions.
Some of the electron charge on the anion is pulled back towards the cation,
The electron field around the anion is distorted.
Describe the factors that determine the polarising power of a cation
Radius:
Smaller radius -> more polarisation
Charge:
Greater charge -> more polarisation
Describe the factors that determine the polarisability of an anion
Radius:
Larger radius -> more polarisation
Charge:
Greater charge -> more polarisation
Define enthalpy change of solution
The enthalpy change when
- 1 mole of a substance is completely dissolved
- in excess water
Define enthalpy change of hydration
The enthalpy change when
- 1 mole of gaseous ions is completely dissolved
- in excess water
Describe the effect of ionic charge and ionic radius on the value of lattice energy
Greater ionic charge, Smaller ionic radius ->
Stronger ionic bonds ->
Greater lattice energy
Describe the effect of ionic charge and ionic radius on the value of enthalpy change of hydration
Greater ionic charge, Smaller ionic radius ->
Stronger attraction with water molecules ->
more exothermic enthalpy change of hydration
State how to predict the solubilty of a ionic compound.
It is soluble if
Enthalpy change of hydration > Lattice enthalpy
