Question

Predict the following species using the VSEPR method:

a) PCl₃
b) CHCl₃
c) SiH₄
d) None of the above

Answer 1

Using the VSEPR model, PCl₃ has a trigonal pyramidal shape due to one lone pair on the central atom, CHCl₃ is tetrahedral with no lone pairs, and SiH₄ is also tetrahedral with no lone pairs.

Step-by-step explanation:

The VSEPR (Valence Shell Electron Pair Repulsion) model is used to predict the molecular geometry of molecules. For each given species, we need to consider the number of bonded atoms and lone pairs on the central atom.

PCl₃ (Phosphorus Trichloride)

Phosphorus has 5 valence electrons and forms three bonds with chlorine atoms, using three electrons, leaving us with one lone pair. This results in a total of 4 electron pairs around the central phosphorus atom, which arranges themselves in a tetrahedral electron pair geometry. The presence of one lone pair however means the observed molecular shape is trigonal pyramidal.

CHCl₃ (Trichloromethane)

Carbon has 4 valence electrons and forms four bonds with one hydrogen and three chlorine atoms. There are no lone pairs on carbon, so the electron pair geometry is tetrahedral and so is the observed molecular shape.

SiH₄ (Silane)

Silicon, like carbon, has 4 valence electrons, all of which are involved in forming single bonds with hydrogen atoms, resulting in no lone pairs. This leads to a tetrahedral electron pair geometry and a tetrahedral molecular shape.