Question

Complete the Lewis structures of the following molecules. Predict the molecular structure, polarity, bond angles, and hybrid orbitals used by the atoms marked by asterisks for each molecule.

Short answer

To analyze the given molecule, follow these steps: 1. Draw the Lewis structure: Count the valence electrons, connect the central atom with single bonds to surrounding atoms, distribute the remaining valence electrons as lone pairs, and form multiple bonds if required. 2. Determine the electron domain geometry: Identify electron domains (bonds and lone pairs) using VSEPR theory. 3. Determine the molecular geometry: Use VSEPR theory to predict the molecular geometry considering only the position of the atoms. 4. Predict the polarity: Compare electronegativity values of bonded atoms to determine if there are polar bonds. Determine if there's a net dipole moment in the molecule. 5. Determine bond angles: Identify ideal bond angles based on the electron domain geometry and account for any deviations due to lone pairs or multiple bonds. 6. Identify hybrid orbitals: Determine the type of hybrid orbitals used by the marked atoms based on the electron domain geometry (e.g., sp for two electron domains, sp2 for three, and sp3 for four). Using these steps, you can complete the Lewis structures, molecular structure, polarity, bond angles, and hybrid orbitals used by the marked atoms for the given molecules.

Step-by-step solution

Draw the Lewis structure

To draw the Lewis structure of the molecule M, we need to follow these steps: 1. Count the total number of valence electrons in the molecule. 2. Write the symbol of the central atom (usually the least electronegative) and connect it with single bonds to surrounding atoms. 3. Distribute the remaining valence electrons as lone pairs to satisfy the octet rule for each atom (except hydrogen, which should have 2 electrons). 4. Check if the central atom has an octet. If not, form multiple bonds (double or triple) to complete the octet.

Determine the electron domain geometry

Identify the number of electron domains (regions of high electron density) around the central atom. This includes bonds (single, double, or triple) and lone pairs. Use the VSEPR (Valence Shell Electron Pair Repulsion) theory to determine the electron domain geometry.

Determine the molecular geometry

Based on the electron domain geometry, determine the molecular geometry by considering only the position of the atoms (ignoring lone pairs). Use the VSEPR theory to predict this geometry.

Predict the polarity of the molecule

Check if the molecule has polar bonds by comparing electronegativity values of bonded atoms. If there are polar bonds, determine if they are symmetrically arranged, canceling each other's effects. If there's a net dipole moment in the molecule, it's polar; otherwise, it's nonpolar.

Determine bond angles

Bond angles are determined based on the electron domain geometry, which was found in step 2. Check the ideal bond angles for the specific electron domain geometry and see if there are any deviations due to the presence of lone pairs or multiple bonds.

Identify hybrid orbitals used by the marked atoms

Based on the electron domain geometry (step 2), determine the type of hybrid orbitals used by the marked atoms. Look for the number of electron domains and find the corresponding hybridization (e.g., two electron domains correspond to sp hybridization, three correspond to sp2, and four correspond to sp3). Using these steps, complete the Lewis structures of the given molecules, predict their molecular structure, polarity, bond angles, and hybrid orbitals used by the marked atoms.

Key concepts

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. It plays a crucial role in determining the physical and chemical properties of that molecule. Once you have drawn the Lewis structure, you can deduce the molecular geometry using VSEPR (Valence Shell Electron Pair Repulsion) theory. This theory suggests that electron pairs, whether they are in bonds or lone pairs, repel each other and will therefore adopt an arrangement that minimizes these repulsions by maximizing the distance between them.
Some common molecular geometries include linear, bent, tetrahedral, trigonal planar, and trigonal pyramidal. Each of these shapes is determined by the number of bonding pairs and lone pairs surrounding the central atom. For instance, if a molecule has two bonding pairs and no lone pairs, it will adopt a linear geometry, whereas a molecule with two bonding pairs and two lone pairs around the central atom will have a bent shape.
Understanding molecular geometry is important not only to predict the shape of a molecule, but also how it will interact with other molecules, its boiling point, reactivity, and even color.

Electron Domain Geometry

Electron domain geometry considers both bonding electron pairs (those involved in bonds) and lone pairs (those not involved in bonds) around the central atom. This geometry is based on the total number of electron domains, which consist of bond pairs as well as lone pairs. The VSEPR model is used to predict this arrangement by assuming that electron domains spread out in 3D space as far from each other as possible to minimize repulsion.
The common electron domain geometries include linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral. Despite similarities in names, electron domain geometry is different from molecular geometry because electron domain geometry treats lone pairs and bonds alike, while molecular geometry focuses only on the position of atoms. For example, a tetrahedral electron domain geometry arises when there are four electron domains. This could lead to various molecular geometries, like tetrahedral or trigonal pyramidal, depending on how many of those domains are lone pairs.
Knowing the electron domain geometry allows chemists to predict the approximate angles between bonds even before knowing which molecular geometry the molecule has.

Hybridization

Hybridization is a concept used to explain the observed shapes of molecules formed by elements like carbon, nitrogen, and oxygen. It describes how atomic orbitals mix to form new, equivalent hybrid orbitals that are degenerate, or of equal energy. These hybrid orbitals are then used to form bonds with other atoms. The type of hybridization depends on the number of electron domains around an atom.
For example, if there are two electron domains, the hybridization of the central atom is sp (one s and one p orbital). When there are three electron domains, the hybridization is sp2 (one s and two p orbitals). With four electron domains, it becomes sp3. Each type of hybridization forms a distinct molecular geometry and affects the angles between bonds, making hybridization a key factor in molecular formation.
This concept is critical for understanding how molecules bond and react, which influences their chemical properties and behaviors. Hybridization enables the prediction of geometric structures and electron distribution in molecules, facilitating a deeper understanding of molecular science.

Bond Angles

Bond angles are the angles formed between two adjacent bonds at an atom in a molecule. These angles help define the geometry and shape of a molecule. By knowing the electron domain geometry established during Lewis structure analysis, one can anticipate the ideal bond angles for a molecule using VSEPR theory.
For example:

• A molecule with a linear electron domain geometry typically has bond angles of 180°.
• A trigonal planar geometry has bond angles of approximately 120°.
• A tetrahedral geometry results in bond angles of about 109.5°.

However, the presence of lone pairs can alter these ideal angles due to increased repulsion. Lone pairs tend to push harder than bonding pairs, reducing the bond angle between other atoms. For instance, in water, the presence of two lone pairs compresses the bond angle from the tetrahedral angle of 109.5° to about 104.5°.
Understanding bond angles helps chemists comprehend molecule shape, actual molecular interactions, and potential energy states critical for chemical reactions. These angles are key in predicting how different molecules will link up during reactions and the products that will form as a result.