Crystal Structure of Sodium Chloride(NaCl) NaCl
is a ionic compound. Hence both Na and Cl are in ionic state. The molecule is under equilibrium because, the attractive force due to ions is balanced by repulsive force due to electron clouds. The Bravais lattice of NaCl is FCC with the basis containing one Na ion
and one Cl ion. The bond length is 2.813A˚ . For each atom there are 6 equidistant nearest neighbours of opposite kind. Hence the coordination number is 6. There are 12 next nearest neighbors of the same kind. The conventional cell which consists of four molecules of NaCl is as shown in the figure. The coordinates of the ions in the conventional cell is as given below. (taking Na ion as origin)
This structure could be considered as the superposed pattern of two interpenetrating Bravais
lattice each made of one type of ion
Crystal structure of Diamond(Allotropic form of carbon)
Diamond is an allotropic form of carbon. The Bravais lattice is an FCC similar to ZnS. There are 18 carbon atoms in the unit cell. 8 at corners, 6 at face centers and 4 at intermediate tetrahedral positions. The unit cell is as shown in the fig. In the unit cell, each carbon
atom bonds to four other carbon atoms in the form of a tetrahedron. Since each atom has four equidistant nearest neighbors the coordination number is 4.This structure could be considered as the superposed pattern of two interpenetrating Bravais FCC lattices each made of Carbon with one displaced from the other along 1/4th of the body diagonal. The interatomic distance is 1.54A˚ and the lattice constant 3.56A˚ .
1. What is the crystal structure of sodium chloride? |
2. How does the crystal structure of sodium chloride contribute to its properties? |
3. What is the crystal structure of diamond? |
4. How does the crystal structure of diamond contribute to its properties? |
5. How do the crystal structures of sodium chloride and diamond differ? |
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