STPM Form 6 Chemistry Solids


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STPM Form 6 Chemistry Solids

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STPM Form 6 Chemistry Solids

  1. 1. Chapter 3 Solids
  2. 2. 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.
  3. 3. Basic Packing System
  4. 4. Lengths and Angles
  5. 5. Basic Crystalline System
  6. 6. Silicondioxide
  7. 7. 1. Cubic
  8. 8. 2. Tetragonal
  9. 9. 3. Hexagonal
  10. 10. 4. Monoclinic
  11. 11. 5. Triclinic
  12. 12. 6. Rhombohedral
  13. 13. 7. Orthorhombic
  14. 14. 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.
  15. 15. Structures of Solids Unit Cells
  16. 16. 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.
  17. 17. Unit Cells
  18. 18. Total 32 crystalline structures
  19. 19. Cubic System1. Simple Cubic StructureSimple cubic structureAtoms only located at the 8 corners
  20. 20. Cubic System2. Body Centered CubicAtoms are arranged at the corners of the cube with another atom at the cube center.
  21. 21. Cubic System3. 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
  22. 22. Examples of Lattice Structure
  23. 23. Structures of Solids Unit Cells
  24. 24. Unit Cells
  25. 25. Coordination numberTotal number of neighbours of a central atom in a molecule or ion
  26. 26. Simple Cubic – KCl Coordination number of 6 52% space 1 atom per unit cell K ClCl K Cl KK Cl
  27. 27. Body-centered Cubic - NaClCoordination number of 82 atoms per unit cell.
  28. 28. Face-centered CubicCoordination number of 12 74.04% space4 atoms per unit cell.
  29. 29. 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.
  30. 30. Structures of SolidsThe Crystal Structure of Sodium Chloride
  31. 31. Structures of SolidsThe Crystal Structure of Sodium Chloride
  32. 32. Commonstructure types Ccp: NaCl structure Also called face centered cubic Halides, oxides, sulfides take this structure often
  33. 33. Allotropes- Same element - Different form Sulphur Carbon Phosphorus Allotropes
  34. 34. Structure ofCarbon Allotropes Diamond
  35. 35. Comparison between Graphite & Diamond Property Diamond GraphiteHybridization sp3 sp2Bond angle 109.5 120Bond length 0.154nm 0.142nmDensity (g/cm3) 3.50 2.25Melting point / K 3823 3925Appearence Bright and sparkling Black and shinyElectrical Non-conductor Conductorconductivity
  36. 36. Structure and bonding affects propertyMelting point - Large amounts of energy is required to break the strong carbon-carbon bondsin graphite and diamond.Solubility - solvent molecules are unable to penetrate the graphite and diamond lattice becauseof the strong covalent bonds between carbon atoms.Hardness - Graphite is soft and has lubricative properties because of the relatively weak Vander Waals forces between layers. This allows the layers to slide over each other. Diamond is veryhard 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 betweenthe layers. Diamond has no mobile electrons to conduct electricity as all the 4 valence electronsof each carbon atom are involved in covalent bonds.
  37. 37. Carbon Nanotubes
  38. 38. Structure ofCarbonnanotubes
  39. 39. Sulphur allotropes
  40. 40. Enantiotropy 95.5 degrees 95.5 degrees
  41. 41. Property S(rhombic) S(monoclinic)Molecular formula S8 S8Colour Lemon Deep yellowStructure Octahedron Long, thin needlesDensity 2.07 1.94Stability Stable below 95.6 Stable above 95.6 degrees degreesMelting point 113 119Solubility in CS2 Soluble Insoluble