1. UNIT CELLS
UNIT CELL – The smallest repeating unit of a crystalline solid
EXP11-1 (of 11)

2. SIMPLE CUBIC UNIT CELL
Length of 1 side of the unit cell:
Full atoms in the unit cell:
2r (r = radius of one particle)
8 × ⅛ = 1
EXP11-2 (of 11)

3. BODY-CENTERED CUBIC UNIT CELLs d s s
Length of 1 side of the unit cell: 4r
___ √3
(8 × ⅛) + 1 = 2
= r√3
______ 3
s2 + d2 = (4r)2
s2 + s2 + s2 = (4r)2
3s2 = 16r2
s2 = 16r2
_____ 3
Full atoms in the unit cell:
EXP11-3 (of 11)

4. The most efficient ways to pack atoms:
1st layer
EXP11-4 (of 11)

5. The most efficient ways to pack atoms:
1st layer
2nd layer
EXP11-5 (of 11)

6. The most efficient ways to pack atoms:
1st layer
2nd layer
3rd layer
This is hexagonal closest packing (hcp), and it makes hexagonal prism unit cells
EXP11-6 (of 11)

7. The most efficient ways to pack atoms:
1st layer
2nd layer
3rd layer
EXP11-7 (of 11)

8. The most efficient ways to pack atoms:
1st layer
2nd layer
3rd layer
This is cubic closest packing (ccp), and it makes face-centered cubic unit cells
EXP11-8 (of 11)

9. FACE-CENTERED CUBIC UNIT CELL
EXP11-9 (of 11)

10. UNIT CELLS FOR IONIC CRYSTALS
Zinc sulfide
Zn =
S =
(8 x 1/8)
(4 x 1)
+ (6 x 1/2)
= 4
 ZnS
EXP11-10 (of 11)

11. UNIT CELLS FOR IONIC CRYSTALS
Sodium chloride
Na =
Cl =
(12 x 1/4)
(8 x 1/8)
+ (1 x 1)
+ (6 x 1/2)
= 4
 NaCl
EXP11-11 (of 11)