The Madelung constant for the fluorite structure is 2.5194. In principal, this r

Question

The Madelung constant for the fluorite structure is 2.5194. In principal, this represents the relative stability of this lattice as compared to other lattice types. It is obtained by considering the attractive and repulsive Coulombic forces that occur when one brings atoms from infinite separation to close proximity in an ionic lattice. The value is obtained by considering each subsequent layer of surrounding atoms until there is no appreciable change in the constant. If only one layer was considered in the fluorite structure (starting from a cation) the Madelung constant would be (to two decimals)___________ which is much greater than the actual constant. If one considers the first two layers together, then the Madelung constant would be (to two decimals)____________ which is much lower than the actual constant (and suggests that the lattice is overall repulsive). Continuing this until infinitely will derive the Maudelung constant..

Explanation / Answer

If only one layer was considered in the fluorite structure (starting from a cation) the Madelung constant would be 3.36 which is much greater than the actual constant. If one considers the first two layers together, then the Madelung constant would be 1.68 which is much lower than the actual constant (and suggests that the lattice is overall repulsive).

Reduced Medulang consatnt for CaF2 is 1.68.

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