STPM Form 6 Chemistry Solids

2. Chapter 3 Solids

3. Types of Solids
Crystalline Solids: highly regular
arrangement of their components [table
salt (NaCl), pyrite (FeS2)]. Crystalline solid
produces the beautiful characteristic shapes
of crystals.
Amorphous solids: considerable disorder
in their structures (glass). Although glass is
a solid, a great deal of disorder exists in its
structure.

7. Basic Packing System

8. Lengths and Angles

9. Basic Crystalline System

13. Silicon
dioxide

14. 1. Cubic

15. 2. Tetragonal

16. 3. Hexagonal

17. 4. Monoclinic

18. 5. Triclinic

19. 6. Rhombohedral

20. 7. Orthorhombic

21. Structures of Solids
• Crystalline solid: well-ordered, definite arrangements of
molecules, atoms or ions.
• Crystals have an ordered, repeated structure.
• The smallest repeating unit in a crystal is a unit cell.
• Unit cell is the smallest unit with all the symmetry of the
entire crystal.
• Three-dimensional stacking of unit cells is the crystal
lattice.

22. Structures of Solids
Unit Cells

23. Structures of Solids
Unit Cells
• Three common types of unit cell.
– Primitive cubic, atoms at the corners of a simple cube,
• each atom shared by 8 unit cells;
– Body-centered cubic (bcc), atoms at the corners of a cube plus
one in the center of the body of the cube,
• corner atoms shared by 8 unit cells, center atom completely enclosed
in one unit cell;
– Face-centered cubic (fcc), atoms at the corners of a cube plus
one atom in the center of each face of the cube,
• corner atoms shared by 8 unit cells, face atoms shared by 2 unit
cells.

24. Unit Cells

25. Total 32 crystalline structures

27. Cubic System
1. Simple Cubic Structure
Simple cubic structure
Atoms only located at the 8 corners

28. Cubic System
2. Body Centered Cubic
Atoms are arranged at the corners of the
cube with another atom at the cube
center.

29. Cubic System
3. Face Centered Cubic (FCC)
Atoms are arranged at the corners and
center of each cube face of the cell.
Atoms are assumed to touch along face
diagonals

33. Examples of Lattice Structure

34. Structures of Solids
Unit Cells

35. Unit Cells

36. Coordination number
Total number of neighbours of a central atom in a molecule or ion

37. Simple Cubic – KCl
Coordination number of 6 52% space
1 atom per unit cell
K Cl
Cl K
Cl K
K Cl

38. Body-centered Cubic - NaCl
Coordination number of 8
2 atoms per unit cell.

39. Face-centered Cubic
Coordination number of 12 74.04% space
4 atoms per unit cell.

40. Structures of Solids
The Crystal Structure of Sodium Chloride
• Two equivalent ways of defining unit cell:
– Cl- (larger) ions at the corners of the cell, or
– Na+ (smaller) ions at the corners of the cell.
• The cation to anion ratio in a unit cell is the same for the
crystal. In NaCl each unit cell contains same number of Na+
and Cl- ions.
• Note the unit cell for CaCl2 needs twice as many Cl- ions as
Ca2+ ions.

41. Structures of Solids
The Crystal Structure of Sodium Chloride

42. Structures of Solids
The Crystal Structure of Sodium Chloride

43. Common
structure types
Ccp: NaCl structure
Also called face
centered cubic
Halides, oxides,
sulfides take this
structure often

44. Allotropes
- Same element - Different form
Sulphur
Carbon Phosphorus
Allotropes

45. Structure of
Carbon Allotropes
Diamond

47. Comparison between
Graphite & Diamond
Property Diamond Graphite
Hybridization sp3 sp2
Bond angle 109.5 120
Bond length 0.154nm 0.142nm
Density (g/cm3) 3.50 2.25
Melting point / K 3823 3925
Appearence Bright and sparkling Black and shiny
Electrical Non-conductor Conductor
conductivity

48. Structure and bonding
affects property
Melting point - Large amounts of energy is required to break the strong carbon-carbon bonds
in graphite and diamond.
Solubility - solvent molecules are unable to penetrate the graphite and diamond lattice because
of the strong covalent bonds between carbon atoms.
Hardness - Graphite is soft and has lubricative properties because of the relatively weak Van
der Waals forces between layers. This allows the layers to slide over each other. Diamond is very
hard because of its rigid tetrahedral arrangement of atoms held by strong carbon-carbon bonds,
giving it a strong and rigid structure.
Electrical conductor - Graphite conducts electricity as it has delocalized electrons between
the layers. Diamond has no mobile electrons to conduct electricity as all the 4 valence electrons
of each carbon atom are involved in covalent bonds.

51. Carbon Nanotubes

52. Structure of
Carbon
nanotubes

54. Sulphur allotropes

55. Enantiotropy
95.5 degrees
95.5 degrees

56. Property S(rhombic) S(monoclinic)
Molecular formula S8 S8
Colour Lemon Deep yellow
Structure Octahedron Long, thin needles
Density 2.07 1.94
Stability Stable below 95.6 Stable above 95.6
degrees degrees
Melting point 113 119
Solubility in CS2 Soluble Insoluble