Shapes of molecules

• Linear have 2 bonding pairs
• Linear has 0 lone pairs
• Linear bond angle is 180
• Example of linear structures are CO2, CS2, HCN, BeF2, BeCl2
• Trigonal planar have 3 bonding pairs
• Trigonal planar have 0 lone pairs
• Bond angle for trigonal planar is 120
• Examples of trigonal planar are BF3, AlCl3, SO3, NO3, CO3²-, BCl3
• Tetrahedral have 4 bonding pairs
• Tetrahedral have 0 pone pairs
• Diagram of tetrahedral

  
• Bond angle for tetrahedral is 109.5
• Examples of tetrahedral are SiCl4, SO4²-, ClO4‐, NH4+
• Trigonal pyramidal have 3 bonding pairs
• Trigonal pyramidal have 1 lone pairs
• Diagram of trigonal pyramidal

  
• The bond angle for trigonal pyramidal is 107
• Examples of trigonal pyramidal are NCl3, PF3, ClO3, H3O+, NH3
• Bent / V-shaped have 2 bonding pairs
• Bent / V-shaped have 2 lone pairs
• Diagram of bent / V- shaped

  
• Bent / V-shaped has a bond angle of 104.5
• Examples of Bent / V-shaped molecules are OCl2, H2S, OF2, SCl2
• Trigonal bipryramidal have 5 bond pairs
• Trigonal bipyramidal have 0 lone pairs
• Diagram of trigonal bipyramidal

  
• Trigonal bipyramidal has a bond angle of 120 and 90
• Examples of trigonal bipyramidal are PCl5
• Octahedral have 6 bond pairs
• Octahedral have 0 lone pairs
• Diagram of octahedral

  
• Octahedral have a bond angle of 90
• Examoles of Octahedral are SF6
• How to explain shapes

  1. State the number of bonding pairs and lone pairs of electrons
  2. State that electron pairs repel and try to get as far a part as possible (or to a position of minimum repulsion)
  3. If there are no lone pairs State that the electron pairs repel equally
  4. If there are lone pairs of electrons then State that lone pairs repel more than bonding pairs
  5. State actual shape and bond angle
• Lone pairs repel more than binding pairs and so reduce bond angles (by about 2.5º per lone pair in the examples mentioned)
• Occasionally more complex shapes are seen that are variations of octahedral and trigonal bipyramidal where some of the bonds replaced with lone pairs. You do not need to leam the names of these but ought to be able to work out these shapes using the method below

  
• XeF4 - Xe has 8 electrons in its outer shell. 4 F's add 4 mmore electrons. This makes a total of 12 ekectrons made up of 4 bond pairs and 2 lone pairs. This means it is a variation of the 6 bond pairs shape (octahedral)

  
• ClF3- Cl has 7 electrons in its outer shell. 3 F's add 3 more electrons this makes a total of 10 electrons made up of 3 bond pairs and 2 lone pairs. This means it's a variation of the 5 bond pair shape (trigonal bupyramidal)

  
• SF4 & IF4+ - I has 7 electrons in its outer shell 4 F's add 4 more electrons Remove one electrons as positively charged. This makes a total of 10 electrons made up of 4 bond pairs and 1 lone pair this means it is a variation of the 5 bond pair shape (trigonal bipyramidal)

  
• An example of the first diagram is BrF5 and an example of the second diagram is I3-