Chapter U2.10, Problem 7E

Interpretation Introduction

Interpretation:The shape of molecule AsH₃ needs to be explained.

Concept Introduction:The Lewis structure of an organic compound represents the bonding of atoms with lone pairs (if any). It indicates the bonds with atoms and also arrangement of atoms in molecule.

Hybridization of any atom indicates the molecular geometry of molecule. The formula to check the hybridization can be written as:

Hybridization = Number of sigma bonds + Number of lone pair

The molecular geometry of molecules with lone pair on central atom is given by VSEPR theory.

Answer to Problem 7E

The shape of arsine is pyramid with bond angle less than 109°.

Explanation of Solution

Given information: The chemical formula of Arsine is AsH_3.

For Lewis structure of AsH₃ molecule, calculate total number of valence electrons:

AsH₃ molecule = 5 electrons in As + 3 x 1 valence electrons in H = 8 electrons

Hybridization = Number of sigma bonds + Number of lone pair

Hybridization of N atom = 3 + 1 = 4 = sp³

Thus, with sp³ hybridization, the molecular shape must be tetrahedral but due to presence of lone pair on central As atom, the geometry must be changed in such a way that the repulsion between lone pair and bond pair must be least. Therefore, the molecular geometry changes to pyramid shape with bond angle less than 109°.

Conclusion

The presence of lone pair on central atom changes the molecular geometry of molecules.