Six Electron Pair Valence Shells

12 for the tetrahedral arrangement of three bonding pairs and a lone pair in the NH3 molecule, showing how this causes the bond angle to be smaller than 109.5°. 

Because lone pair domains are larger and more spread out around the central core than bonding pair domains, the angles between bonding pair domains are smaller than the angles between lone pair domains. Consequently  

In molecules with lone pairs, bond angles are smaller than the ideal values associated with a given number of equivalent pairs, and they decrease with increasing number of lone pairs. 

Molecule Bond Angle Molecule Bond Angle 

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