Unit cell of CaF2

1
Unit cell of CaF2
(black ball) represents Fluoride ion
(white ball) represents calcium ion
2
Unit Cell
The unit cell is the smallest portion of the
crystal which contains all the details of the
crystal without repetition. If an unit cell is
repeated in 3-dimensions, then the repeating
pattern reproduces the whole lattice of the
crystal .
3
Content of unit cell
Particles completely within the unit cell are not
shared with others and are counted 1 per cell.
4
Content of unit cell
1. Particles on the face are shared equally
between two adjacent unit cells and hence are
counted 1/2 for each .
5
Content of unit cell
2. Particles at a corner are shared equally among
eight adjacent unit cells and hence are counted
1/8 for each .
No. of Ca 2 ½ (6) 1/8 (8) 4 No. of F
- 8
6
Coordination Number
The coordination number of a particular atom or
ion is the no. of adjacent atoms or ions in
direct contact with the particular atom or ion.
Ca2
F-
C.N. of Ca2 C.N. of F- 8 4
7
Summary
Ions are places at each corner and on each of
the 6 faces. The Unit call is Faced-Centred
Cubic. Molecular Formula CaF2
The End
6S Au Yee Ki (1) 6S Wong Chung Hing (21)