Experimental and theoretical lattice energy

Question 1

the ‘experimental lattice energy’ is

Answer 1

the value of the lattice energy calculated using the experimentally determined values which make up Born-Haber cycles

Question 2

the type of lattice structure and the inter-ionic distance can be found by

Answer 2

X-ray crystallography

Question 3

the assumptions made when calculating the value for the lattice energy of an ionic compound are: (3)

Answer 3

→that the ions are in contact with one another
→that the ions are perfectly spherical
→that the charge on each ion is evenly distributed around the centre so that each ion can be considered as point charges

Question 4

the theoretical lattice energy is calculated by

Answer 4

using the principles of electrostatics and the assumptions combined with X-ray crystallography

Question 5

the covalency in bonding is caused by

Answer 5

→polarisation of the anion (negative) by the cation (positive), so the anion is polarised
→this results in a distortion of the electron density within the anion
→this means a higher electron density is produced near the cation
→there is therefore some electron density between the two ions
→this is a degree of covalent bonding in the compound

Question 6

the two main factors affecting the extent to which an anion is polarised by a cation (Fajan’s Rules) are:

Answer 6

that polarisation will be increased by:
→a high charge and a small size of the cation (high CHARGE DENSITY of the cation
→a high charge and LARGE size of the anion

Question 7

the charge density of a cation is (calculation)

Answer 7

the charge divided by the surface area of the ion

Question 8

the surface area of a spherical ion is =

Answer 8

4πr2