Question

There are two different molecules with the formula \(\mathrm{N}_{2} \mathrm{~F}_{2}\) Is either molecule polar? Explain.

Short answer

Explain your reasoning. Answer: Yes, the \(\mathrm{N}_{2}\mathrm{F}_{2}\) molecule is polar. This is because its molecular geometry is bent, and the electronegativity difference between the nitrogen and fluorine atoms creates polar bonds. The bent shape of the molecule prevents the cancellation of the polar bonds, resulting in an overall dipole moment and a polar molecule.

Step-by-step solution

Identify the molecular geometry of both molecules

There are two possible structures for the \(\mathrm{N}_{2}\mathrm{F}_{2}\) molecules: 1) The linear structure: N-F-N-F or F-N-N-F 2) The bent structure: F | N-N | F To determine the molecular geometry, we utilize the VSEPR (valence shell electron pair repulsion) theory. In the case of \(\mathrm{N}_{2}\mathrm{F}_{2}\), both nitrogen atoms have three electron pairs in their valence shell: two single N-F bonds and one lone electron pair (as each nitrogen atom has 5 electrons in its valence shell - 3 are used for the N-N bond, and 2 are in the N-F bonds). As a result, the molecular geometry will be bent. Thus, the bent structure is the correct geometry for the \(\mathrm{N}_{2}\mathrm{F}_{2}\) molecule.

Determine the electronegativity of each atom

Now that we know the molecular geometry, we need to determine the electronegativity of the atoms in the molecule. Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. The Pauling electronegativity values for nitrogen (N) and fluorine (F) are: - Nitrogen (N): 3.04 - Fluorine (F): 3.98 Keep these values in mind for the next step, as they will help us determine if there is a dipole moment in the \(\mathrm{N}_{2}\mathrm{F}_{2}\) molecule.

Determine if there is a dipole moment

To determine if there is a dipole moment in the molecule, we must consider the difference in electronegativity and the molecular geometry established in steps 1 and 2. In the bent \(\mathrm{N}_{2}\mathrm{F}_{2}\) structure, the bonds between the nitrogen (N) and fluorine (F) atoms have a significant difference in electronegativity (3.98 - 3.04 = 0.94). This difference creates a polar bond, where the electrons are pulled more strongly towards the more electronegative fluorine atom. Additionally, due to the bent molecular geometry, the two polar bonds do not cancel out, and the molecule as a whole shows an unequal distribution of electron density and a resulting dipole moment.

Conclusion

Based on the analysis of the molecular geometry, atom electronegativities, and the dipole moment, we can conclude that the bent \(\mathrm{N}_{2}\mathrm{F}_{2}\) molecule is polar.

Key concepts

VSEPR Theory

Understanding the shape of a molecule is crucial in predicting its properties, and that's where Valence Shell Electron Pair Repulsion (VSEPR) theory comes in. It states that electron pairs around a central atom will arrange themselves as far apart as possible to minimize repulsion.

To apply VSEPR theory, count the number of electron groups (bonds and lone pairs) around the central atom. In our exercise example, each nitrogen in N_2F_2 has three electron groups, leading to a bent shape.

The VSEPR model is a powerful tool for predicting the 3D structure of molecules, which is a key determinant in understanding polarity, reactivity, and other properties.

Electronegativity

Electronegativity is a concept that measures how strongly an atom can attract or hold onto electrons. It's a relative scale, with fluorine (F) being the most electronegative element.

In the molecule N_2F_2, we have nitrogen (N) with an electronegativity of 3.04 and fluorine (F) with 3.98. The significant difference (0.94) between them indicates that the bonding electrons are more strongly attracted to the fluorine atoms. This creates an imbalance in electron density that is essential in determining the molecule's polarity.

Dipole Moment

A dipole moment arises from differences in electronegativity between bonded atoms which create a polar bond. It's a vector quantity, meaning it has both magnitude and direction – from the less electronegative atom to the more electronegative atom.

In the N_2F_2 molecule's bent geometry, the polar bonds between N and F create dipole moments that do not cancel out due to the molecular geometry. Thus, the overall molecule has a net dipole moment, leading to its polarity.

Molecular Geometry

Molecular geometry, determined by the spatial arrangement of atoms in a molecule, affects many properties, including polarity.

In the case of N_2F_2, the bent shape, resulting from VSEPR theory application, causes the individual polar bonds' dipole moments to add up vectorially to a net dipole moment. If the molecule were linear, these moments could cancel out, but the bent geometry does not allow for this, resulting in a polar molecule.

Chemical Bonding

Chemical bonding describes the attraction between atoms that enables the formation of chemical compounds. Bonding can be covalent, where atoms share electron pairs, or ionic, where electrons are transferred from one atom to another.

In our N_2F_2 example, the N-F bonds are covalent but polarized due to the difference in electronegativity. This polarization contributes to the molecule's overall polarity. Understanding the different types of bonding and how they affect molecular structure is essential in chemistry.