The experimentally measured H–X–H bond angle in NH₃ is 107.3°
CHEMISTRY · Multi-part · AP · Chemistry · Compound Structure and Properties · Compound Structure and Properties
Problem
The experimentally measured H–X–H bond angle in NH₃ is 107.3°, whereas the corresponding angle in PH₃ is 93.5°.
Although both molecules are commonly described as having the same electron-domain geometry, their bond angles differ markedly.
(1) Identify the electron-domain geometry and write a set of hybrid orbitals that could be used to describe bonding at the nitrogen and at the phosphorus atom, respectively.
(2) Predict which of the two central atoms (N or P) will undergo the greater degree of hybridization (i.e., has hybrid orbitals that deviate more from pure atomic orbitals). Justify your answer qualitatively in terms of energy considerations for orbital mixing.
(3) Using your reasoning from part (b), explain quantitatively why the H–P–H bond angle is substantially smaller than the H–N–H bond angle. Your explanation should integrate (i) lone-pair versus bonding-pair repulsion strengths and (ii) the effectiveness of hybridization in second-period versus third-period elements.