Question

What do each of the following sets of compounds/ions have in common with each other? See your Lewis structures for Exercises 107 through 110 . a. \(\mathrm{XeCl}_{4}, \mathrm{XeCl}_{2}\) b. \(\mathrm{ICl}_{5}, \mathrm{TeF}_{4}, \mathrm{ICl}_{3}, \mathrm{PCl}_{3}, \mathrm{SCl}_{2}, \mathrm{SeO}_{2}\)

Short answer

In Set a, both $\mathrm{XeCl}_{4}$ and $\mathrm{XeCl}_{2}$ have the same central atom (Xenon) and peripheral atom (Chlorine) and a total of five electron domains for the central atom. In Set b, all compounds have nonmetal central atoms with non-zero numbers of lone pairs forming bonds with halogens or chalcogens.

Step-by-step solution

Drawing Lewis structures

Draw the Lewis structures for each of the compounds in both sets. Make sure to show all the lone pairs and bonding pairs of electrons for each element to better understand the molecular geometry.

Analyzing molecular geometries and electron domains

Analyze the molecular geometries of each compound by looking at their Lewis structures. Count the number of electron domains, which include bonding pairs, lone pairs, and single electrons.

Identifying common features

Now that we have analyzed the molecular geometries, we will identify the common features among the compounds in each set. Set a: 1. \(\mathrm{XeCl}_{4}\) - the Xe atom has 2 lone pairs and 4 bonding pairs 2. \(\mathrm{XeCl}_{2}\) - the Xe atom has 3 lone pairs and 2 bonding pairs Both compounds in Set a have a similar central atom (Xenon, Xe) and the same peripheral atom (Chlorine, Cl). The Xe atom in both compounds also has a total of five electron domains (counting both lone pairs and bonding pairs). Set b: 1. \(\mathrm{ICl}_{5}\) - 5 bonding pairs, 1 lone pair 2. \(\mathrm{TeF}_{4}\) - 4 bonding pairs, 2 lone pairs 3. \(\mathrm{ICl}_{3}\) - 3 bonding pairs, 2 lone pairs 4. \(\mathrm{PCl}_{3}\) - 3 bonding pairs, 1 lone pair 5. \(\mathrm{SCl}_{2}\) - 2 bonding pairs, 2 lone pairs 6. \(\mathrm{SeO}_{2}\) - 2 bonding pairs, 2 lone pairs All these compounds in Set b exhibit a trend: they are all nonmetals forming compounds with halogens or chalcogens. They also have a non-zero number of lone pairs on the central atom (I, Te, P, S, and Se). In conclusion, the common features in each set of compounds are as follows: Set a: They have the same central atom (Xe) and peripheral atom (Cl), with a total of five electron domains for the central atom. Set b: All compounds have nonmetal central atoms with non-zero numbers of lone pairs forming bonds with halogens or chalcogens.

Key concepts

Lewis Structures

The foundation of predicting the shape and reactivity of molecules starts with Lewis structures. These diagrammatic representations allow us to see how atoms in a molecule are connected and how electrons are distributed. To draw a Lewis structure, we signify each atom with its chemical symbol and use dots to symbolize the valence electrons, with lines representing shared electron pairs or bonds.

When we analyze the provided compounds, we approach the Lewis structures by first considering the valence electrons of each atom. For the Xenon (Xe) compounds, we know Xe as a noble gas has eight valence electrons to work with. The Chlorine (Cl) atoms each contribute seven. Then we determine how these electrons are shared (bonding pairs) or remain unpaired (lone pairs). In both \(\mathrm{XeCl}_{4}\) and \(\mathrm{XeCl}_{2}\), the bonding patterns and lone pairs reveal the connectivity and possible shapes of these molecules, which is crucial for understanding their molecular geometries.

Molecular Geometries

Understanding molecular geometry involves looking beyond the two-dimensional Lewis structures to visualize molecules in three dimensions. Molecular geometry dictates the arrangement of atoms in space, shaped by the electron domains which include both bonding pairs (shared electrons) and lone pairs (non-shared electrons).

To deduce the molecular geometry, the VSEPR (Valence Shell Electron Pair Repulsion) theory is employed, which states that electron domains will arrange themselves as far apart as possible to minimize repulsion. For example, if we consider \(\mathrm{XeCl}_{4}\), its electron domain geometry would be octahedral, with its molecular geometry being square planar due to the two lone pairs causing a shift from the idealized shape. The molecular geometry of each compound helps us predict the compound’s properties such as polarity and reactivity.

Lone Pairs and Bonding Pairs

When discussing electron domains, we distinguish between two types: lone pairs and bonding pairs. A bonding pair is a set of electrons shared between two atoms forming a bond. In contrast, a lone pair is a pair of valence electrons that are not shared with another atom and remain localized on a single atom.

Lone pairs take up more space around the central atom than bonding pairs because they are attracted to only one nucleus, causing more repulsion and a greater impact on the molecular geometry. For instance, the \(\mathrm{ICl}_{5}\) molecule includes one lone pair on the central Iodine (I) which influences its molecular shape, deviating from the symmetry it would exhibit without the lone pair. Recognizing the role of lone pairs and bonding pairs is crucial in predicting the structure and behavior of molecules.

Central and Peripheral Atoms

In any given molecule, we can identify central and peripheral atoms. The central atom is typically the one capable of making the most connections and is often the atom with the lowest electronegativity. Peripheral atoms are those bonded to the central atom.

The central atoms in the given exercise, such as Xenon (Xe) in the first set and Iodine (I), Tellurium (Te), Phosphorus (P), Sulfur (S), and Selenium (Se) in the second set, are surrounded by peripheral atoms like Chlorine (Cl) and Oxygen (O). It’s the central atom that primarily determines the overall geometry of the molecule since it’s the one with electron domains that need to be minimized in terms of mutual repulsion. Understanding the role of these atoms is pivotal in constructing accurate molecular models and in the interpretation of molecular data such as bond angles and lengths.