Many structures of phosphorus- and sulfur-containing...

Many structures of phosphorus- and sulfur-containing compounds are drawn with some $\mathrm{P}=\mathrm{O}$ and $\mathrm{P}=\mathrm{S}$ bonds. These bonds are not the typical $\pi$ bonds we've considered, which involve the overlap of two $p$ orbitals. They result instead from the overlap of a $d$ orbital on the phosphorus or sulfur atom with a $p$ orbital on oxygen. This type of $\pi$ bonding is sometimes used as an explanation for why $\mathrm{H}_{3} \mathrm{PO}_{3}$ has the first structure below rather than the second: (FIGURE CAN'T COPY) Draw a picture showing how a $d$ orbital and a $p$ orbital overlap to form a $\pi$ bond.

Many structures of phosphorus- and sulfur-containing compounds are drawn with some $\mathrm{P}=\mathrm{O}$ and $\mathrm{P}=\mathrm{S}$ bonds. These bonds are not the typical $\pi$ bonds we've considered, which involve the overlap of two $p$ orbitals. They result instead from the overlap of a $d$ orbital on the phosphorus or sulfur atom with a $p$ orbital on oxygen. This type of $\pi$ bonding is sometimes used as an explanation for why $\mathrm{H}_{3} \mathrm{PO}_{3}$ has the first structure below rather than the second:
(FIGURE CAN'T COPY)
Draw a picture showing how a $d$ orbital and a $p$ orbital overlap to form a $\pi$ bond.

Key Concepts

p Orbitals

These are atomic orbitals with a dumbbell shape that are oriented along specific axes (x, y, and z). They are key in forming bonds due to their directional nature, and when they overlap side-by-side with other orbitals, they yield ? bonds. In the context of pi bonding with d orbitals, the p orbital on an electronegative atom such as oxygen provides the necessary electron density for the sideways, lateral overlap with an appropriate d orbital.

d Orbitals

d Orbitals are more complex in shape compared to s or p orbitals and can have cloverleaf or other geometries. In main-group elements further down the periodic table, these orbitals can participate in bonding, especially for elements like phosphorus and sulfur. The involvement of a d orbital in bonding allows for the formation of bonds that are not standard sigma or pure p-p pi bonds, particularly by overlapping with a p orbital to form a pi bond.

Pi Bonding

Pi bonds are formed when two atomic orbitals overlap sideways, rather than head-on as in sigma bonds. This sideways overlap results in electron density concentrated above and below the plane of the bonded atoms. In structures involving phosphorus or sulfur, a d orbital can overlap with a p orbital to produce a ? bond, contributing to double bond characteristics between the atoms.

Orbital Overlap

Orbital overlap is a fundamental concept governing chemical bond formation. When orbitals from two atoms overlap, they share electron density, forming a bond. In traditional ? bonding, the overlap is between p orbitals; however, when a d orbital overlaps with a p orbital, the interaction still results in a ? bond, though the spatial distribution and energy levels are influenced by the different shapes and orientations of the orbitals involved.

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