13.1.2 - Experimental and Theoretical Lattice energy Flashcards
What is inter-ionic distance?
The distance from the centres of ions in a lattice
What are assumptions that are made for theoretical lattice energy?
Ions are in contact
Ions are perfect spheres
Charge is distributed evenly around the centre of an ion.
Why is there often a difference between experimental and theoretical lattice energies?
Due to covalent character.
The bigger the discrepancy, the greater the extent of the covalent character.
What causes covalent character in an ionic lattice?
The polarisation of the anion by the cation.
The cations pulls electrons from the anion towards it.
What features of a cation affect polarisation of an anion?
Ionic radius
Ionic charge
Why are the experimental and theoretical values for lattice energy closer for AgF than AgBr?
Br is bigger so more easily polarised
Increasing covalent character
How are theoretical and Experimental lattice energies obtained?
Experimental - Using a Born Haber cycle
Theoretical - Principles of electrostatics
(ions are in contact, perfect spheres, charge evenly distributed)
What is polarising power?
The ability of a cation to attract electrons from the anion towards itself.
If a cation has a large polarising power, what can be said about its ionic charge and size?
Large charge
Small radius
Is there more covalent character in NaCl or MgCl2?
MgCl2
Charge density of magnesium ions is greater.
So Mg polarises Cl more.
Is there more covalent character in AgF or AgI?
AgI
Ionic radius of iodide is greater than fluoride
Iodide more easily polarised
