Is N2 Paramagnetic Or Diamagnetic

Is N₂ Paramagnetic or Diamagnetic? Understanding Molecular Magnetism

Determining whether a molecule is paramagnetic or diamagnetic is crucial in understanding its behavior in a magnetic field. This seemingly simple question—is N₂ paramagnetic or diamagnetic?—opens the door to a deeper understanding of molecular orbital theory, electron configuration, and the fundamental principles of magnetism. This article will delve into the details, providing a comprehensive explanation accessible to both beginners and those seeking a more in-depth understanding.

Introduction

Paramagnetism and diamagnetism are two fundamental properties of matter related to its interaction with a magnetic field. Diamagnetic substances are weakly repelled by a magnetic field because all their electrons are paired. In contrast, paramagnetic substances are weakly attracted to a magnetic field due to the presence of unpaired electrons. These unpaired electrons possess a net magnetic moment, making them susceptible to external magnetic fields. The question of whether N₂, or nitrogen gas, is paramagnetic or diamagnetic hinges on the electron configuration of the molecule and how these electrons are arranged within its molecular orbitals.

Understanding Molecular Orbital Theory

To answer whether N₂ is paramagnetic or diamagnetic, we need to delve into the world of molecular orbital theory. Unlike atomic orbitals, which describe the behavior of electrons within individual atoms, molecular orbitals describe the behavior of electrons in a molecule. These molecular orbitals are formed by the linear combination of atomic orbitals (LCAO) of the constituent atoms. In the case of N₂, two nitrogen atoms each contribute seven electrons to the molecular orbitals.

The formation of molecular orbitals in N₂ involves the 2s and 2p atomic orbitals of each nitrogen atom. The 2s orbitals combine to form two molecular orbitals: a bonding σ2s orbital (lower in energy) and an antibonding σ*2s orbital (higher in energy). Similarly, the 2p orbitals combine to form three bonding and three antibonding molecular orbitals. The 2p orbitals interact in two ways:

• Sigma (σ) bonds: One 2p orbital from each nitrogen atom overlaps head-on, forming a σ2p bonding orbital and a σ*2p antibonding orbital.
• Pi (π) bonds: The remaining two 2p orbitals from each nitrogen atom overlap sideways, forming two degenerate π2p bonding orbitals and two degenerate π*2p antibonding orbitals. "Degenerate" means they have the same energy level.

Electron Configuration of N₂

With a total of 14 valence electrons (7 from each nitrogen atom), these electrons fill the molecular orbitals according to the Aufbau principle and Hund's rule. The order of filling is as follows:

σ2s < σ2s < σ2p < π2p < π2p < σ*2p

Following this order, the electron configuration of N₂ is:

(σ2s)²(σ*2s)²(σ2p)²(π2p)⁴

Notice that all electrons are paired. The two electrons in the σ2s bonding orbital are paired, as are the two in the σ*2s antibonding orbital, the two in the σ2p bonding orbital, and the four in the two degenerate π2p bonding orbitals.

Conclusion: N₂ is Diamagnetic

Because all the electrons in the N₂ molecule are paired, there is no net magnetic moment. This means that N₂ is diamagnetic. It will be weakly repelled by a magnetic field. The presence of paired electrons in all molecular orbitals effectively cancels out any individual magnetic moments.

Detailed Explanation of Paramagnetism and Diamagnetism

To fully appreciate why N₂ is diamagnetic, let's look more closely at the origin of paramagnetism and diamagnetism.

• Diamagnetism: Diamagnetism arises from the interaction of an external magnetic field with the orbital motion of electrons. Even in the absence of an external field, electrons are in constant motion around the nucleus, generating tiny magnetic fields. When an external field is applied, these orbital motions are slightly altered, inducing a magnetic moment that opposes the external field. This opposition is the basis of diamagnetic repulsion. It is a weak effect present in all atoms and molecules.

• Paramagnetism: Paramagnetism is a much stronger effect than diamagnetism and occurs when atoms or molecules have unpaired electrons. Each unpaired electron possesses a magnetic moment due to its spin. When an external magnetic field is applied, these unpaired electrons align their magnetic moments with the field, leading to a net attraction. The strength of paramagnetism depends on the number of unpaired electrons and the strength of their individual magnetic moments.

Further Considerations: Bond Order and Stability

The molecular orbital diagram also helps us understand the strength of the N₂ triple bond. The bond order is calculated as:

Bond Order = (Number of electrons in bonding orbitals - Number of electrons in antibonding orbitals) / 2

For N₂, the bond order is (8 - 2) / 2 = 3, indicating a very strong triple bond. This high bond order contributes to the stability and inertness of nitrogen gas.

Frequently Asked Questions (FAQ)

• Q: What happens if we add or remove electrons from N₂? A: Adding or removing electrons would change the electron configuration and potentially lead to unpaired electrons, making the resulting ion paramagnetic.

• Q: Are all diatomic molecules diamagnetic? A: No. Oxygen (O₂), for example, is paramagnetic because it has two unpaired electrons in its antibonding π*2p orbitals.

• Q: How can we experimentally verify if a substance is diamagnetic or paramagnetic? A: This can be done using a Gouy balance or a similar magnetic susceptibility apparatus. These instruments measure the force exerted on a sample in a magnetic field, allowing for the determination of its magnetic properties.

• Q: What are some other examples of diamagnetic molecules? A: Many molecules with all paired electrons are diamagnetic, including CO₂, H₂O, and CH₄.

Conclusion

In conclusion, N₂ is diamagnetic due to the absence of unpaired electrons in its molecular orbitals. Its electron configuration, derived from molecular orbital theory, clearly demonstrates that all valence electrons are paired, resulting in a net magnetic moment of zero. This understanding highlights the importance of molecular orbital theory in predicting the magnetic properties of molecules and offers a deeper insight into the fundamental principles governing chemical bonding and molecular behavior. By understanding the electron configuration and the principles of paramagnetism and diamagnetism, we can accurately predict and explain the magnetic properties of a wide range of substances.