Question

Predict the molecular structure (including bond angles) for each of the following. (See Exercises 111 and \(112 .\) ) a. \(\mathrm{ICl}_{5}\) b. \(\mathrm{XeCl}_{4}\) c. \(\mathrm{SeCl}_{6}\)

Short answer

In conclusion, the molecular structures and bond angles for the given molecules are as follows: a. \(\mathrm{ICl}_{5}\): Square pyramidal, bond angles around 90 degrees and 120 degrees b. \(\mathrm{XeCl}_{4}\): Square planar, bond angles around 90 degrees c. \(\mathrm{SeCl}_{6}\): Octahedral, bond angles around 90 degrees and 180 degrees

Step-by-step solution

Identify the central atom, bond electron pairs, and lone electron pairs for each molecule.

For each molecule, we'll first identify the central atom and count the number of bond electron pairs and lone electron pairs on it. a. \(\mathrm{ICl}_{5}\): Central atom: Iodine (I) Bond electron pairs: 5 (one bond with each of the 5 chlorine atoms) Lone electron pairs: 1 (as 7 - 5 = 2; corresponds to one lone electron pair) b. \(\mathrm{XeCl}_{4}\): Central atom: Xenon (Xe) Bond electron pairs: 4 (one bond with each of the 4 chlorine atoms) Lone electron pairs: 2 (as 8 - 4 = 4; corresponds to two lone electron pairs) c. \(\mathrm{SeCl}_{6}\): Central atom: Selenium (Se) Bond electron pairs: 6 (one bond with each of the 6 chlorine atoms) Lone electron pairs: 0 (as 6 - 6 = 0; corresponds to zero lone electron pairs)

Predict the molecular structure and bond angles using VSEPR theory.

Now, we will use the VSEPR notation AXE, where A represents the central atom, X represents the bond electron pairs, and E represents the lone electron pairs. Then, we'll determine the molecular structure based on it. a. \(\mathrm{ICl}_{5}\): VSEPR notation: AX5E1 Molecular structure: Square pyramidal Bond angles: Approximately 90 degrees between equatorial atoms and axial atoms; approximately 120 degrees between two equatorial atoms. b. \(\mathrm{XeCl}_{4}\): VSEPR notation: AX4E2 Molecular structure: Square planar Bond angles: Approximately 90 degrees between any two adjacent chlorine atoms. c. \(\mathrm{SeCl}_{6}\): VSEPR notation: AX6E0 Molecular structure: Octahedral Bond angles: 90 degrees between any two adjacent chlorine atoms; 180 degrees between any two opposite chlorine atoms. In conclusion, the molecular structures and bond angles for the given molecules are as follows: a. \(\mathrm{ICl}_{5}\): Square pyramidal, bond angles around 90 degrees and 120 degrees b. \(\mathrm{XeCl}_{4}\): Square planar, bond angles around 90 degrees c. \(\mathrm{SeCl}_{6}\): Octahedral, bond angles around 90 degrees and 180 degrees

Key concepts

Molecular Structure

Molecular structure is the three-dimensional arrangement of atoms within a molecule. Imagine a molecule as a small structure where each atom or group of atoms hold a specific spot. This specific arrangement affects the molecule's behavior and properties.

To predict the molecular structure, chemists often use the VSEPR (Valence Shell Electron Pair Repulsion) theory. This theory helps us understand how electron pairs around a central atom repel each other and push atoms into specific geometries. By knowing the number of bond pairs and lone pairs, we can predict structures like linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral, and others.

Take the example of \(\text{ICl}_5\). It forms a square pyramidal structure because the lone pair on the iodine forces the five bonded chlorine atoms into a pyramid-like shape with a square base. Each molecule has its unique shape influenced by the atoms it contains and how they are connected.

Bond Angles

Bond angles are the angles formed between three atoms across at least two bonds. These angles determine how close or far atoms are from each other in a molecule. For instance, in a tetrahedral structure, the ideal bond angles between adjacent atoms are about 109.5 degrees.

Bond angles can vary depending on the molecular structure and the presence of lone pairs. In \(\text{SeCl}_6\), with its octahedral structure, the bond angles are perfect 90 degrees and 180 degrees due to the symmetric shape. However, in \(\text{ICl}_5\), the presence of a lone pair distorts the angles, so they differ slightly from perfect values.

Understanding bond angles gives crucial insights into the spatial configuration of a molecule and influences things like polarity and reactivity. Pay close attention to these angles when determining the potential behavior of a chemical compound.

Electron Pairs

In the context of VSEPR theory, electron pairs are key in determining molecular structure. These include both bonding pairs, which are shared between atoms to form bonds, and lone pairs, which belong solely to one atom and do not participate in bonding.

Every electron pair, whether bonding or lone, repels other electron pairs. This can be visualized as a kind of electron ‘crowding’ that shapes the overall structure of the molecule. For example, in \(\text{XeCl}_4\), the lone pairs on xenon push the bonding pairs into a square planar arrangement, maintaining balance and minimizing repulsion.

Recognizing the number and types of electron pairs on the central atom allows chemists to predict the bonding arrangement and angles, tremendously impacting molecule shape and function.

Central Atom

The central atom in a molecule is the primary atom to which other atoms are bonded. It usually has the highest ability to form bonds, often being less electronegative than the surrounding atoms.

Identifying the central atom is crucial in applying VSEPR theory. Once it's identified, you can calculate how many electron pairs might surround it to help predict the shape of the molecule. For instance, in \(\text{XeCl}_4\), xenon acts as the central atom, accommodating four bonding pairs of electrons from chlorine and having two lone pairs.

Understanding the central atom's role helps in predicting not just the shape but also the reactivity and properties of the molecule. In complex molecules, ensuring the right atom is chosen as the central atom is the first step in providing credible structural predictions.