Predict the shape of AsCl_3.
From its Lewis structure, we see that AsCl_3 has four electron groups with three bonded atoms.
\begin{array}{c}\underset{\cdot\cdot}{\overset{\cdot\cdot}{\text{:Cl:}}}\underset{\cdot\cdot}{\overset{\cdot\cdot}{\text{As:}}}\underset{\cdot\cdot}{\overset{\cdot\cdot}{\text{Cl:}}}\\\underset{\cdot\cdot}{\text{:Cl:}}\end{array}The electron-group geometry is tetrahedral, but with the central atom bonded to three Cl atoms, the shape is trigonal pyramidal.