Answer to Question #154703 in General Chemistry for Youssef

Question

Use tge vsepr model to predict the geometry of AsH3

Answer 1

In AsH3, As is the central atom

As is in group 5A hence it has (1 x 5 = 5 valency electrons).

H is in group 1A hence they have (3 x 1 = 3 valency electrons)

Total valence electrons = 5+3=8 valence electrons.

This means that there are 4 electron domains, suggesting a tetrahedral electron domain geometry. However, one electron domain is a lone pair of electrons. The 3 hydrogens and one lone pair of electrons make As Sp³ hybridized. So it has a slightly different shape because of the lone pair of electrons. molecular geometry is therefore different; it is called trigonal pyramidal.

This is because the lone pair would want as much space as it can get, and the largest angle it could have from the other atoms would be on top of the molecule, leaving the other hydrogens in a trigonal pyramidal shape.