Page 45 - Microsoft PowerPoint - lecture1.ppt

2.3 Basic structure types

Bonding in ionic structures – Coulomb interaction

Classic picture of ionic bonding: cations donate electrons to anions thus

each species fullfills the octet rule.

+
i.e. Na + F → Na + F -

Interaction between anions and cations: Coulomb interactions.

Coulomb potential

z z e 2 of an ion pair

V  A   N
AB
4 AB
r
0

V : Coulomb potential (electrostatic potential)
AB
A: Madelung constant (depends on structure type)

-19
z: charge number, e: elementary charge = 1.60210 C
2
2
: dielectric constant (vacuum permittivity) = 8.8510 -12 C /(Nm )
o
r : shortest distance between cation and anion
AB
23
N: Avogadro constant = 6.02310 mol -1