Page 48 - Microsoft PowerPoint - lecture1.ppt

2.3 Basic structure types

Lattice energy of a ionic structure

1) Set the first derivative of the sum to zero

2) Substitute B-parameter of repulsive part

2
z
e
0
  .(V AB  Born )  0   z   0 N 1 (  1 )
Min
A
V
L
4
r
n
L
0
-1
• typical values, measured (calculated) [kJ mol ]:

• NaCl: –772 (-757); CsCl: -652 (-623)

• measured means by Born Haber cycle (later)

• fraction of Coulomb interaction at r : ~ 90%
0
• missing in our lattice energy calculations:

• zero point energy

• dipole-dipole interaction

• covalent contributions, example: AgCl: -912 (-704)