Question

Predict the molecular structure for each of the following. (See Exercises 105 and \(106 .\) ) a. \(\mathrm{BrFI}_{2}\) b. \(\mathrm{XeO}_{2} \mathrm{~F}_{2}\) c. \(\mathrm{TeF}_{2} \mathrm{Cl}_{3}^{-}\) For each formula there are at least two different structures that can be drawn using the same central atom. Draw all possible structures for each formula.

Short answer

In summary, the possible molecular structures for the given formulas are as follows: a. BrFI2: - Structure 1: Br with two F atoms and one I atom bonded, with a lone pair. - Structure 2: Br with two I atoms and one F atom bonded, with a lone pair. b. XeO2F2: - Structure 1: Two O atoms occupy the axial positions and two F atoms occupy the equatorial positions. - Structure 2: Two F atoms occupy the axial positions and two O atoms occupy the equatorial positions. c. TeF2Cl3-: - Structure 1: One F and three Cl atoms occupy the equatorial plane while another F atom occupies the axial position. - Structure 2: Two F atoms and two Cl atoms occupy the equatorial plane while another Cl atom occupies the axial position.

Step-by-step solution

1. BrFI2

First, we need to determine the central atom, which is the least electronegative atom (excluding Hydrogen). In BrFI2, the central atom is Br. Now, let's count the number of electron domains, including bonding pairs and lone pairs. Br has 7 valence electrons, and each of the F and I atoms contributes 1 electron for bonding. Therefore, we have a total of 9 electrons to distribute. That means there are 4 electron domains (3 bonding pairs and 1 lone pair) around the Br atom. Using the VSEPR model, the electron geometry for 4 electron domains is tetrahedral. However, since it is specified that there are at least two different structures that can be drawn, we can arrange the F and I atoms differently: - Structure 1: Br with two F atoms and one I atom bonded, with a lone pair. - Structure 2: Br with two I atoms and one F atom bonded, with a lone pair.

2. XeO2F2

The central atom for XeO2F2 is Xe. Now, let's count the number of electron domains. Xe has 8 valence electrons, and each of the O and F atoms contributes 1 electron for bonding. Therefore, we have a total of 12 electrons to distribute. That means there are 5 electron domains (4 bonding pairs and 1 lone pair) around the Xe atom. Using the VSEPR model, the electron geometry for 5 electron domains is trigonal bipyramidal. We should consider two different arrangements of O and F atoms: - Structure 1: Two O atoms occupy the axial positions and two F atoms occupy the equatorial positions. - Structure 2: Two F atoms occupy the axial positions and two O atoms occupy the equatorial positions.

3. TeF2Cl3-

The central atom for TeF2Cl3- is Te. Now, let's count the number of electron domains. Te has 6 valence electrons and as an anion, it has one more added electron to its outer shell, making it 7. Each of the F and Cl atoms contributes 1 electron for bonding. Therefore, we have a total of 12 electrons to distribute. That means there are 6 electron domains (5 bonding pairs and 1 lone pair) around the Te atom. Using the VSEPR model, the electron geometry for 6 electron domains is octahedral. We should consider two different arrangements of F and Cl atoms: - Structure 1: One F and three Cl atoms occupy the equatorial plane while another F atom occupies the axial position. - Structure 2: Two F atoms and two Cl atoms occupy the equatorial plane while another Cl atom occupies the axial position. Now, you can depict the structures in two-dimensional Lewis structures or three-dimensional molecular geometry models.

Key concepts

VSEPR model

The Valence Shell Electron Pair Repulsion (VSEPR) model is an essential tool in predicting the geometry of molecules. It helps us understand how electron pairs, both bonding and lone pairs, arrange themselves around a central atom. The basic premise of the VSEPR model is that electron pairs will arrange themselves as far apart as possible to minimize repulsion.

This model identifies the electron domain geometry, which is crucial in determining the overall shape of the molecule. For instance, a molecule with four electron domains typically forms a tetrahedral shape, while one with five domains might take on a trigonal bipyramidal shape. The VSEPR model allows chemists to predict different possible molecular structures, providing insight into potential physical and chemical properties.

Electron domain

The concept of electron domains is fundamental when applying the VSEPR model. An electron domain includes all areas of electron density around the central atom—this includes both bonding pairs (those involved in bonding) and lone pairs (non-bonded electrons).

Counting electron domains helps to identify the electron geometry around the central atom. For example, in the molecule XeO iF i_3, five electron domains were noted, which led to a trigonal bipyramidal geometry. Recognizing the number of electron domains is a stepping stone in visualizing the 3D structure of a molecule and determining how the atoms will likely arrange themselves based on electron pair interactions.

Lewis structure

The Lewis structure is a way to represent molecules showing all the atoms, bonds, and lone pairs. It’s a crucial tool for predicting molecular geometry and is often the starting point when using the VSEPR model. In drawing a Lewis structure, we first determine the total number of valence electrons and distribute them among the atoms to satisfy the octet rule as much as possible.

Once you have the Lewis structure, you can identify the central atom, count bonding and lone pairs, and figure out the electron domain geometry. These structures give a 2D representation of the molecule but serve as a guide, setting the stage for applying the VSEPR model to predict its 3D shape and possible isomers.

Bonding pairs

Bonding pairs are pairs of electrons shared between atoms, forming a covalent bond. They play a critical role in the shape and structure of molecules. Each bonding pair helps to form an electron domain around the central atom. However, they are influenced by the presence of other electron domains, which can alter bonding angles and affect the overall shape of the molecule.

In the molecule BrFI i_2, the central bromine atom forms bonds with both fluorine and iodine, creating three bonding pairs. In such molecular structures, the position of these bonding pairs, in relation to lone pairs, is crucial to the spatial arrangement and resulting VSEPR-predicted geometry.

Lone pairs

Lone pairs refer to valence electrons that do not participate in bonding and remain localized on a single atom. They are significant in determining molecular shape as they occupy space and exert repulsion on bonding electrons, often leading to deviations from ideal bond angles.

When applying VSEPR theory, lone pairs are considered in establishing the electron domain geometry. For example, in the case of TeF i_2Cl i_3^-, the presence of lone pairs on the tellurium atom plays a role in achieving an octahedral arrangement overall. Lone pairs are influential as they tend to repel more strongly than bonding pairs, thus altering the molecular geometry significantly.