Problem 31 - Chemistry in 30 days

Question

Which one of the following is paramagnetic? (a) \(\mathrm{O}_{2}\) (b) \(\mathrm{N}_{2} \mathrm{O}\) (c) \(\mathrm{He}\) (d) \(\mathrm{NH}_{3}\)

Step-by-Step Solution

Answer

Option (a) O_2 is paramagnetic as it has unpaired electrons.

Step 1: Understand Paramagnetism

Paramagnetism occurs when a substance has one or more unpaired electrons in its electronic configuration. These unpaired electrons create a magnetic moment, making the substance weakly attracted to a magnetic field.

Step 2: Analyzing Option (a) O_2

The molecular orbitals of O_2 show that it has two unpaired electrons in the ^*_{2p} orbitals. This makes O_2 paramagnetic as these unpaired electrons contribute to a net magnetic moment.

Step 3: Analyzing Option (b) N_2O

In N_2O, nitrogen and oxygen atoms form a stable molecule with a full pairing of electrons in their molecular orbitals, indicating no unpaired electrons. Therefore, N_2O is diamagnetic.

Step 4: Analyzing Option (c) He

Helium (He) has a filled 1s orbital, with both electrons paired. As a result, there are no unpaired electrons, making He diamagnetic.

Step 5: Analyzing Option (d) NH_3

In the molecule NH_3, all electrons are paired in its molecular orbitals, and thus, it has no unpaired electrons. Hence, NH_3 is diamagnetic.

Step 6: Choosing the Paramagnetic Substance

Among the options, O_2 is the only molecule that has unpaired electrons, making it paramagnetic.

Key Concepts

Understanding Unpaired Electrons

Unpaired electrons play a crucial role in determining the magnetic properties of molecules and atoms. An electron is considered unpaired if it does not have another electron with the opposite spin in the same orbital.
The presence of unpaired electrons usually suggests paramagnetic behavior, meaning the substance will be attracted to magnetic fields.
In this context, it's essential to look at each option's electronic configuration to determine the presence of unpaired electrons.

• Unpaired electrons create a magnetic dipole or a small magnet-like effect.
• Materials with unpaired electrons are often paramagnetic.
• Pay close attention to electron pairing when analyzing magnetic properties.

Even one unpaired electron can cause a material to become paramagnetic, as seen in substances like oxygen. Recognizing these electrons involves understanding molecular orbital theories and electron distributions.

Exploring Molecular Orbitals

The concept of molecular orbitals is key to understanding the distribution of electrons in a molecule. Molecular orbitals are formed when atomic orbitals combine as atoms bond together to form a molecule. They can be classified as bonding, antibonding, or non-bonding orbitals, each contributing differently to the stability of a molecule.
These orbitals are essential when predicting the paramagnetic or diamagnetic nature of a substance.

• Bonding orbitals have lower energy and usually no unpaired electrons, contributing to stability.
• Antibonding orbitals can have unpaired electrons, potentially making the molecule paramagnetic.
• The presence of unpaired electrons in antibonding orbitals can result from incomplete electron pairing.

For instance, in oxygen ( O_2 ), the presence of unpaired electrons in the σ^*_{2p} antibonding orbitals is responsible for its paramagnetic nature. Understanding the arrangement of these electrons helps in predicting magnetic properties.

Interpreting Magnetic Properties

Magnetic properties are determined by the electron arrangement in atoms or molecules. They tell us whether a substance is attracted or repelled by a magnetic field. These properties depend heavily on the presence of unpaired electrons and their respective molecular orbitals. Substances are generally classified as either paramagnetic or diamagnetic based on these criteria.

• Paramagnetic substances have unpaired electrons leading to attraction by a magnetic field. 😃
• Diamagnetic substances have all paired electrons and are repelled by magnetic fields.
• Analyzing molecular orbitals can reveal the magnetic nature of a compound.

In our example, O_2 is paramagnetic because of its two unpaired electrons, meaning it will be attracted to a magnetic field, while ext{N}_2 ext{O} , He, and ext{NH}_3 are diamagnetic. Understanding these principles helps in predicting and explaining the magnetic behavior of various substances.