Week 4

• What is normally the central atom in a shape?

  First atom in formula or least electronegative atom (shares its electrons)
• What are the 6 shapes of molecules?

  • Linear (sp)
  • Trigonal (sp2)
  • Tetrahedral (sp3)
  • Square Planar (sp2d)
  • Trigonal Bipyramidal (sp3d)
  • Octahedral (sp3d2)
• How do you predict molecular shapes (VSEPR)?

  • Count central atom valence electrons
  • Add electrons used by other atoms to make bonds to central atom
  • Adjust for charge
  • Adjust for multiple bonding
  • Number of electron pairs predicts shape
• What are Lewis structures?


  Predict covalent bonding between atoms
• How do you draw Lewis structures?

  • Count valence electrons
  • Decide on central atom
  • Assemble bonding framework with single bonds
  • Place 3 electron pairs on each outer non-H atom
  • Assign remaining valence electrons to central atom
  • Minimise formal charges
• Who does the octet rule apply to?


  First row P block
• What is hybridisation of atomic orbitals?


  Mixing atomic orbitals to make new ones that point in useful directions

  Orbitals point towards the atoms making bonds
• What are SP hybridised orbitals?


  Need 2 hybridised orbitals at 180 degrees to eachother to fit linear molecules

  Use 2 atomic orbitals to make 2 hybridised atomic orbitals (s + px)

  (py & pz don't hybridise here)
• What are SP2 hybridised orbitals?


  Need 3 hybridised orbitals at 120 degrees to eachother to fit trigonal planar molecule

  Combine S & 2 p orbitals (px + py)

  (pz unaffected)
• What are SP3 hybridised orbitals?


  Combine S, Px, Py & Pz orbitals to make 4 equal hybridised orbitals to fit tetrahedral molecule