Regarding the ozone (O3) molecule: a) What is the electron geometry? b) What is the molecular geometry?
The Correct Answer and Explanation is:
Correct Answer:
a) Electron Geometry: Trigonal planar
b) Molecular Geometry: Bent (or Angular)
Detailed Explanation
The ozone (O₃) molecule consists of three oxygen atoms bonded together. To understand its geometry, it is essential to analyze the arrangement of electron pairs around the central oxygen atom using the Valence Shell Electron Pair Repulsion (VSEPR) theory.
Electron Geometry:
The electron geometry considers both bonding pairs and lone pairs of electrons around the central atom. For O₃, one oxygen atom is placed in the center, connected to two other oxygen atoms. The central oxygen has a total of three regions of electron density: two bonding regions (from the two sigma bonds with the other oxygen atoms) and one lone pair. According to VSEPR theory, three regions of electron density around a central atom arrange themselves in a trigonal planar geometry to minimize repulsion.
Molecular Geometry:
While electron geometry focuses on all electron regions, molecular geometry describes the actual shape formed by the atoms in the molecule, ignoring lone pairs. In O₃, the lone pair on the central oxygen atom influences the shape by pushing the bonded oxygen atoms closer together. This results in a bent or angular molecular shape, similar to the structure of water (H₂O), although the bond angles are slightly different.
The bond angle in ozone is approximately 117 degrees, slightly less than the ideal 120 degrees of a perfect trigonal planar structure due to lone pair repulsion being greater than bonding pair repulsion.
Additional Notes:
Ozone exhibits resonance, meaning its actual structure is a hybrid of two resonance forms where the double bond shifts between the two oxygen atoms. This gives both oxygen-oxygen bonds a partial double-bond character, making the bond lengths equal and intermediate between a single and double bond.
In summary, ozone’s electron geometry is trigonal planar based on three regions of electron density, but its molecular shape is bent due to the presence of a lone pair on the central atom.
