Using the VSEPR theory, predict the molecular structure of...

Using the VSEPR theory, predict the molecular structure of each of the following molecules or ions containing multiple bonds.
a. $\mathrm{SO}_{2}$
b. $\mathrm{SO}_{3}$
c. $\mathrm{HCO}_{3}^{-}$ (hydrogen is bonded to oxygen)
d. HCN

Key Concepts

VSEPR Theory

VSEPR (Valence Shell Electron Pair Repulsion) theory is a model used to predict the geometry of molecules based on the premise that electron pairs around a central atom will arrange themselves as far apart as possible to minimize repulsive forces. This theory considers both bonding pairs and lone pairs in determining the spatial arrangement of atoms in a molecule.

Electron Domain Geometry

Electron domain geometry refers to the three-dimensional arrangement of all electron pairs (bonding and lone pairs) around a central atom. The count of these domains determines the idealized geometry, which forms the basis for predicting the molecular structure of the compound.

Treatment of Multiple Bonds

In VSEPR theory, multiple bonds such as double and triple bonds are treated as a single electron domain. This simplification allows for a consistent approach to predicting molecular shapes by counting each multiple bond as one region of electron density, despite the fact that they involve more than one pair of electrons.

Lone Pairs and Their Influence on Molecular Geometry

Lone pairs, or non-bonding electron pairs, occupy space around the central atom and exert repulsive forces that can distort the ideal bond angles predicted by the electron domain geometry. Their presence often leads to deviations in molecular geometry from the ideal shape, influencing the overall structure observed in molecules.

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