The structure of \(\mathrm{XeO}_{3}\) is (A) linear (B) planar (C) pyramidal (D) T-shaped

Understanding the shape of molecules is crucial in chemistry because it determines how molecules interact and react with each other. Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. The Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict these shapes by assuming that electron pairs around a central atom will arrange themselves as far apart as possible to minimize repulsion.

VSEPR theory predicts the molecular geometry by taking into account the number of bonding and non-bonding electron pairs (lone pairs) around the central atom. For instance, when there are four electron pairs as in the case of methane (CH4), the molecular geometry is tetrahedral. However, if one of these pairs is a lone pair, as in ammonia (NH3), the geometry is trigonal pyramidal.

In summary, the molecular geometry is not only a result of the bonded atoms but also significantly influenced by the lone pairs of electrons, which can change the expected angle between bonds and hence the shape of the molecule.

The structure of xenon trioxide (XeO3) is a fascinating example of how noble gases can form compounds despite their inert nature. Xenon, with eight valence electrons, forms bonds with three oxygen atoms. Its structure can be deduced through a step-by-step approach involving the VSEPR theory.

Given that xenon is the central atom surrounded by three oxygen atoms with one lone pair, the VSEPR theory guides us to a tetrahedral electron pair geometry as the starting point. Since one of the vertices of this tetrahedral is occupied by a lone pair, the actual shape of XeO3 is trigonal pyramidal. This shape reflects the repulsion between the lone pair of electrons and the bonded pairs, causing the molecule to adopt a geometry that minimizes these repulsions. The XeO3 molecule, therefore, does not lie flat but rather has a three-dimensional structure that is best described as pyramidal.

Electron pair geometry is closely related to molecular geometry, but they are not the same thing. It encompasses the spatial arrangement of all electron pairs (bonding and lone pairs) around the central atom of a molecule. The electron pair geometry is based on the idea that electron pairs, whether they are in bonds or are lone pairs, repel each other and tend to be as far apart as possible.

The common electron pair geometries include linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral. Each geometry corresponds to a certain number of electron pairs. For example, a linear electron pair geometry suggests two electron pairs, while tetrahedral geometry indicates four pairs. In the case of XeO3, the presence of three bonding pairs and one lone pair of electrons surrounding the xenon atom results in a tetrahedral electron pair geometry. However, the molecular geometry, which describes the arrangement of atoms (and not lone pairs), is trigonal pyramidal.