Shape of molecules and ions

• Electron pairs must be a bonded pair or a lone pair, the pairs can be decided by drawing a dot and cross diagram
• Electron repulsion theory

  • Each pair of electrons around and atom will repel all other electron pairs
  • The pairs of electrons will therefore take up a position as far away as possible to minimise any repulsion in a molecule
• Non-linear

  BP: 2

  LP: 2

  Angle: 104.5
• Linear

  BP: 2

  LP: 0

  Angles: 180
• Trigonal Planar

  BP: 3

  LP: 0

  Angle: 120
• Pyramidal

  BP: 3

  LP: 1

  Angle: 107
• Tetrahedral

  BP: 4

  LP: 0

  Angle: 109.5
• Square Planar

  BP: 4

  LP: 2

  Angle: 90
• Trigonal Bipyramidal

  BP: 5

  LP: 0

  Angle: 120, 90
• Octahedral

  BP: 6

  LP: 0

  Angle: 90
• Some molecules have unshared pairs of electrons; electrons not part of a covalent bond
• Repulsion


  BP-BP < LP-BP < LP-LP

  BP-BP has the least repulsion

  LP-LP has the greatest repulsion