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Creative Chemistry Molecular Models

The Tetrahedral Department

What is here?

You can see ball-and-stick models of methane, ammonia and water. Why have I chosen these?

  • All three molecules have four pairs of electrons around their central atom.
  • As a result, they all have a tetrahedral arrangment of electron pairs around the central atom.
  • The bond angle in methane, CH4, is the tetrahedral angle, i.e. 109.5 (109 28').
  • Ammonia, NH3, contains a lone pair of electrons, which repels the bonding electrons to give a bond angle of 107. The atoms have a trigonal pyramidal arrangement.
  • Water, H2O, contains two lone pairs of electrons, which repel each other as well as the bonding electrons, to give a bond angle of 104.5. The atoms have a bent line arrangement.

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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