Question

Refer to the Integrative Example. A compound related to nitryl fluoride is nitrosyl fluoride, FNO. For this molecule, indicate (a) a plausible Lewis structure and (b) the geometric shape. (c) Explain why the measured resultant dipole moment for FNO is larger than the value for \(\mathrm{FNO}_{2}\).

Short answer

The Lewis structure for FNO molecule has N in the middle bonded with F on one side and O on the other, with N-F having a single bond, and N-O having a double bond. It has a bent geomertric shape due to three regions of electron density around the central N atom. The dipole moment for FNO is larger than that of \(\mathrm{FNO_{2}}\) because FNO, being a bent molecule, has a net dipole moment, whereas in \(\mathrm{FNO_{2}}\), the linear structure can lead to dipole cancellation leading to a smaller dipole moment overall.

Step-by-step solution

Finding a Plausible Lewis Structure

In order to draw a plausible Lewis structure for FNO, you need to calculate the total number of valence electrons in the molecule. The molecule is composed of fluorine (F) which has 7 valence electrons, nitrogen (N) with 5 valence electrons, and oxygen (O) also with 6 valence electrons. This gives a total of 18 valence electrons. A plausible Lewis structure would be N in the middle bonded with F on one side and O on the other, with N-F having a single bond, and N-O having a double bond. Remaining electrons are then distributed as lone pairs on F and O, both having three lone pairs.

Determining Geometric Shape

The central atom (N) has three regions of electron density (one single bond, one double bond, and one lone pair). Applying the VSEPR theory, the molecule has a bent shape or V-shape with the angle slightly less than 120 degrees due to the presence of the lone pair.

Explaining Dipole Moment Comparison

\(\mathrm{FNO}\) being a bent molecule, it has a dipole moment since the pull of electron density is not symmetric around the molecule. On the other hand, for \(\mathrm{FNO_{2}}\), if the molecule is in a linear configuration, it could have a resultant dipole moment of zero as the pull of electron density from each side could cancel each other. Hence, \(\mathrm{FNO}\) is expected to have a larger dipole moment when compared to \(\mathrm{FNO_{2}}\).

Key concepts

VSEPR Theory

VSEPR, which stands for Valence Shell Electron Pair Repulsion, is a model used to predict the geometry of individual molecules. It is based on the idea that electron pairs surrounding an atom will repel each other and will arrange themselves to be as far apart as possible. This helps chemists understand the shape of a molecule, which is essential in predicting its chemical behavior and reactivity.

In the case of nitrosyl fluoride (FNO), the central atom is nitrogen. By examining the types of bonds and lone pairs around this nitrogen atom, VSEPR theory helps us determine the molecular shape. FNO features one single bond to fluorine (F), one double bond to oxygen (O), and a lone pair of electrons. According to VSEPR theory, three regions of electron density are arranged in a way that minimizes repulsion, giving FNO a bent or "V-shaped" geometry. This geometry results in a bond angle slightly less than 120 degrees.

Dipole Moment

A dipole moment is a measure of the separation of electrical charges within a molecule. It occurs when there is an unequal distribution of electrons between the atoms, leading to regions of positive and negative charge. A molecule with a higher dipole moment has a stronger separation of charges.

For nitrosyl fluoride (FNO), the presence of a bent shape contributes to its dipole moment. Since the molecule is asymmetrical due to its V-shape, the electrons are not evenly distributed across the molecule. The dipole moment arises because the electric charge is more toward the more electronegative oxygen atom, while fluorine also pulls on the electrons but less so than oxygen, resulting in an overall dipole across the molecule.

Comparatively, \( \mathrm{FNO}_{2} \), if linear or less bent, tends to balance out any dipole moments if the pulls of electron density oppose one another evenly. Thus, the dipole moment for FNO could be larger, as the electron density in the comparatively smaller molecule does not cancel out efficiently, making FNO have a noticeable net charge separation.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule, crucial for understanding its physical and chemical properties. Geometry influences properties such as polarity, reactivity, color, phase of matter, and magnetism.

In examining nitrosyl fluoride (FNO), the molecular geometry is crucial for understanding its behavior. As determined through VSEPR theory, FNO exhibits a bent geometry due to the lone pair of electrons and the arrangement of atoms around the nitrogen center. These structural details inform predictions about the molecule's reaction tendencies and polarity.

• The bent shape of the molecule indicates that it is polar, meaning it will have intermolecular attractions and react distinctly compared to non-polar molecules.
• The angles between the atoms affect the overall spatial orientation, indicating how FNO might interact with other molecules and surfaces.
• Understanding molecular geometry also aids in predicting the kinds of bonds formed during reactions, elucidating how molecules like FNO will behave under different chemical conditions.

In summary, molecular geometry provides insights into both the physical layout and the intrinsic behaviors of molecules, playing a pivotal role in chemistry.