Question

Which statement best captures the fundamental idea behind VSEPR theory? Explain what is wrong with the statements you do not choose. \begin{equation}\begin{array}{l}{\text { a. The angle between two or more bonds is determined primarily by }} \\ {\text { the repulsions between the electrons within those bonds and other }} \\ {\text { (lone pair) electrons on the central atom of a molecule. Each of these electron groups }} \\ {\text { (bonding electrons or lone pair electrons)lowers its potential energy by maximizing }} \\ {\text { its separation from other electron groups, thus determining the geometry of the molecule. }} \\ {\text { b. The angle between two or more bonds is determined primarily by the repulsions between }} \\\ {\text { the electrons within those bonds. Each of these bonding electrons lowers its potential energy }} \\ {\text { by maximizing its separation from other electron groups, thus determining the geometry }} \\ {\text { of the molecule }} \\ {\text { c. The geometry of a molecule is determined by the shapes of the overlapping orbitals }} \\ {\text { that form the chemical bonds. Therefore, to determine the geometry of a molecule, }} \\ {\text { you must determine the shapes of the orbitals involved in bonding.}}\end{array}\end{equation}

Short answer

Statement (a) best captures the fundamental idea behind VSEPR theory, because it considers the repulsions between all electron groups (bonding and lone pairs) and accurately explains their influence on molecular geometry.

Step-by-step solution

Understand VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) theory posits that electron groups (bonding and lone pairs) around a central atom organize themselves as far apart as possible to minimize repulsions. This organization dictates the molecular shape.

Analyze Statement (a)

Statement (a) accurately describes VSEPR theory, acknowledging repulsions between all forms of electron groups (bonding and lone pairs) and their influence on molecular geometry.

Analyze Statement (b)

Statement (b) inaccurately limits the repulsions to only the electrons within the bonds (bonding electrons) and does not consider lone pairs, which play a critical role in determining molecular geometry according to VSEPR theory.

Analyze Statement (c)

Statement (c) incorrectly attributes molecular geometry to the shapes of the overlapping orbitals involved in chemical bonds, which is a concept more closely related to molecular orbital or hybridization theories rather than VSEPR theory.

Choose the Correct Statement

After evaluating all statements, statement (a) best captures the essence of VSEPR theory. Statements (b) and (c) do not comprehensively or accurately describe the fundamental idea behind VSEPR theory.

Key concepts

Molecular Geometry

Molecular geometry is the three-dimensional arrangement of atoms within a molecule. It's a critical aspect of chemical science because it influences the physical and chemical properties, such as reactivity, polarity, color, phase of matter, and magnetism. The shape of a molecule is determined primarily by the positions of its electrons because they carry negative charges that repel one another due to their like charges.

Through VSEPR theory, we can predict the geometric structure by considering electron pairs as point charges that repel each other, arranging themselves as far apart as possible around the central atom. By understanding the concept of electron pair repulsion, as described in statement (a) of the exercise, we can accurately forecast the molecular geometry. These geometries could be linear, bent, trigonal planar, tetrahedral, and more, each corresponding to a specific combination of bond pairs and lone pairs on the central atom.

Electron Pair Repulsion

Electron pair repulsion is the force that drives the VSEPR theory and hence determines the shape of the molecule. To visualize this concept, imagine electron groups, both bonding and non-bonding pairs, repelling each other akin to how magnets with the same poles push away from one another. This repulsion is a result of the electrons' negative charge.

In the context of the provided exercise, acknowledging the presence of lone pair electrons, as statement (a) does, is fundamental to understanding how these repulsions shape the molecule. Lone pairs occupy more space than bonding pairs because they are attracted to only one nucleus as opposed to two, leading to a larger electron cloud. This causes increased repulsion and therefore a greater impact on molecular shape compared to bonding electrons alone.

Chemical Bonding

Chemical bonding is the process that enables atoms to combine and form molecules, which is inextricably linked to the idea of molecular geometry and VSEPR theory. Bonding can occur in several ways, such as covalent, ionic, or metallic bonds, with electrons playing the vital role.

The statement (c) from the exercise addresses the bonding concept but misconstrues it by focusing on the shapes of overlapping orbitals rather than electron pair repulsions. While orbital shapes do matter in chemical bonding and can influence molecular geometry through hybridization, it's the VSEPR theory that straightforwardly clarifies how electron groups adopt the arrangement that minimizes repulsions, resulting in the observed molecular structure. Therefore, correct comprehension of chemical bonding within the VSEPR model necessitates a recognition of the overall electron structure, including both the bonding interactions and the steric requirements of electron pairs.