Problem 31 - Chemistry in 30 days

Question

Which of the following is diamagnetic? (a) \(\mathrm{Na}_{2} \mathrm{O}_{2}\) (b) \(\mathrm{KO}_{2}\) (c) both (d) none

Step-by-Step Solution

Answer

(a) Na_{2}O_{2} is diamagnetic.

Step 1: Understand Magnetic Properties

Diamagnetic substances have no unpaired electrons and are not attracted by a magnetic field, while paramagnetic substances have one or more unpaired electrons and are attracted by a magnetic field.

Step 2: Analyze Na_{2}O_{2}

Sodium peroxide (Na_{2}O_{2}) contains the peroxide ion (O_2^{2-}). The peroxide ion has all paired electrons, leading to diamagnetic properties for Na_{2}O_{2}.

Step 3: Analyze KO_{2}

Potassium superoxide (KO_{2}) contains the superoxide ion (O_2^-). The superoxide ion has an unpaired electron, making KO_{2} paramagnetic.

Step 4: Compare Options

Only Na_{2}O_{2} is diamagnetic because it has paired electrons; KO_{2} is paramagnetic due to an unpaired electron in the superoxide ion.

Key Concepts

Magnetic Properties

Magnetic properties explain how a material reacts to a magnetic field. These properties are primarily determined by the presence or absence of unpaired electrons in substances.

A diamagnetic substance is one that does not have any unpaired electrons. Such substances are pushed out from magnetic fields or show no attraction. Essentially, they create an internal magnetic field in the opposite direction when exposed to an external one. Examples of diamagnetic materials include water, most organic compounds, and even salts like \( ext{Na}_2 ext{O}_2\).

On the other hand, paramagnetic substances are ones that contain one or more unpaired electrons. These unpaired electrons cause weak attractions to magnetic fields, often aligning themselves with the poles of the external magnet. Common paramagnetic materials include oxygen and salts like \( ext{KO}_2\). Understanding these properties is crucial when predicting the behavior of compounds in a magnetic field, which is often based on their electron configurations.

Peroxide Ion

The peroxide ion is a significant player when examining magnetic properties. Represented as \( ext{O}_2^{2-}\), this ion consists of two oxygen atoms sharing a pair of electrons.

In this ion, each oxygen atom contributes electrons to a bond. All the electrons here are paired, leading to a closed-shell configuration. This paired nature of electrons in \( ext{O}_2^{2-}\) results in zero magnetic moments, rendering the compounds containing this ion, such as \( ext{Na}_2 ext{O}_2\), diamagnetic.

Interestingly, the presence of peroxide ions in a compound ensures diamagnetism, due to the absence of any unpaired electrons. This means these compounds do not align with magnetic fields, as there is no "magnetic distress" caused by unpaired electrons. This characteristic is instrumental in chemical identification and behavior prediction.

Superoxide Ion

The superoxide ion, represented by \( ext{O}_2^{-}\), is an intriguing subject in chemistry, particularly in the study of magnetic properties. Unlike the peroxide ion, the superoxide ion hosts a notable unpaired electron.

This unpaired electron is crucial, as it causes the entire ion to exhibit paramagnetism. Paramagnetic materials like \( ext{KO}_2\), containing the superoxide ion, will be drawn into a magnetic field because the unpaired electron has a magnetic moment.

The superoxide ion's single unpaired electron makes it highly reactive, a property that chemists leverage for various reactions. This reactivity and magnetic property are vital for understanding the behavior of molecules in a magnetic field and predicting their potential chemical pathways. Thus, unlike their diamagnetic counterparts, superoxide ion-containing compounds are actively magnetic and involved in diverse chemical processes.