Phosphorus forms both PCl5 (a stable gas) and POCl3 (a stable liquid)
CHEMISTRY · Multi-part · AP · Chemistry · Compound Structure and Properties · Compound Structure and Properties
Problem
Phosphorus forms both PCl5 (a stable gas) and POCl3 (a stable liquid). The central atom in each molecule is bonded to five surrounding atoms or groups.
Investigate the bonding and stability of these two molecules.
(a) For PCl5, draw a Lewis diagram that minimizes formal charges and state the formal charge on each atom.
(b) For POCl3, two nonequivalent Lewis diagrams can be drawn:
• Structure I: P doubly bonded to O (P═O) and singly bonded to three Cl atoms.
• Structure II: P singly bonded to O and singly bonded to three Cl atoms, with appropriate lone pairs on O.
Draw both structures and calculate all formal charges.
(c) Using your formal-charge calculations and electronegativity considerations, identify which structure (I or II) better represents POCl3 in the gas phase. Provide a clear justification.
(d) Compare the ability of phosphorus to form PCl5 versus POCl3 by discussing how the presence of the highly electronegative O atom influences the distribution of electron density and the overall stability of the molecule.