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The Trigonal Bipyramidal Department

What is here?

You can see ball-and-stick models of PF5, SF4, ClF3 and I3. Why have I chosen these?

  • All four molecules have five pairs of electrons around their central atom.
  • As a result, they all have a trigonal bipyramidal arrangment of electron pairs around the central atom.
  • The bond angles are 90º between axial atoms and equatorial atoms, and 120º between equatorial atoms.
  • Phosphorus pentafluoride, PF5, has no lone pair of electrons.
  • Sulphur tetrafluoride, SF4, has one lone pair of electrons.
  • Chlorine trifluoride, ClF3, has two lone pair of electrons.
  • The I3ion has three lone pairs of electrons. Therefore, the electron pairs still have a trigonal bipyramidal arrangement, but because the three equatorial atoms are “missing”, the atoms have a linear arrangement. The bond angle is 180º.

The lone pairs of electrons show up as a small ball on these models. The molecules are animated, but if you want to stop them, right-click to bring up the menu and deselect Animate. Try using the left mouse button to turn the models around in different directions.
 

Molecular modelling applet courtesy of ChemAxon Ltd

 

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