Problem 167 - A Complete Resource Book in Chemistry for JEE Main

Question

Match the following Column-I Column-II (a) \(\mathrm{O}_{2}^{2+}\) (p) Paramagnetic (b) \(\mathrm{O}_{2}^{+}\) (q) Diamagnetic (c) \(\mathrm{O}_{2}^{-}\) (r) Bond order \(=1\) (d) \(\mathrm{O}_{2}^{2-}\) (s) Bond order \(=1.5\) (t) Stable ion under appropriate conditions in the gas or liquid phase.

Step-by-Step Solution

Answer

(a) No exact match, (b) p, (c) p and s, (d) q, r, and t.

Step 1: Understand the properties of molecular oxygen

Oxygen ( O _2 ) can gain or lose electrons forming ions like O _2 ^{2+}, O _2 ^{+}, O _2 ^{-}, and O _2 ^{2-}. We need to match each ion with its corresponding magnetic property or bond order provided in Column-II.

Step 2: Determine magnetic property (paramagnetic/diamagnetic) and bond order of each ion

- O _2 ^{2+} has 10 electrons. Removing two electrons compared to O _2 leaves no unpaired electrons, making it diamagnetic with a bond order of 3. No exact match in options. - O _2 ^{+} has 11 electrons, one unpaired electron, making it paramagnetic with a bond order of 2.5 (option p matches). - O _2 ^{-} has 13 electrons, one unpaired electron, making it paramagnetic with a bond order of 1.5 (options p and s match). - O _2 ^{2-} has 14 electrons, no unpaired electrons, making it diamagnetic with a bond order of 1 (option q and r match). It is stable under certain conditions (option t could also match).

Step 3: Match each oxygen ion to its properties

- (a) O _2 ^{2+} doesn't have a direct option match. - (b) O _2 ^{+} matches with (p) Paramagnetic. - (c) O _2 ^{-} matches with both (p) Paramagnetic and (s) Bond order = 1.5. - (d) O _2 ^{2-} matches with (q) Diamagnetic and (r) Bond order = 1, it can also be matched with (t) Stable ion.

Step 4: Final matching list

- (a) O _2 ^{2+} : Does not have an exact match. - (b) O _2 ^{+} : (p) Paramagnetic - (c) O _2 ^{-} : (p) Paramagnetic, (s) Bond order = 1.5 - (d) O _2 ^{2-} : (q) Diamagnetic, (r) Bond order = 1, (t) Stable ion.

Key Concepts

Bond Order

When we talk about bond order in the context of molecular orbital theory, we're understanding the strength and stability of a bond between atoms in a molecule. The bond order is calculated as half the difference between the number of bonding electrons and antibonding electrons:\[ \text{Bond Order} = \frac{(\text{number of bonding electrons}) - (\text{number of antibonding electrons})}{2} \]A higher bond order typically signifies a stronger bond. For example, in the step-by-step solution regarding oxygen ions:

• For \(\mathrm{O}_{2}^{2+}\), the bond order is 3, indicating a strong bond.
• For \(\mathrm{O}_{2}^{+}\), the bond order is 2.5.
• For \(\mathrm{O}_{2}^{-}\), the bond order is 1.5.
• For \(\mathrm{O}_{2}^{2-}\), the bond order is 1, showing a weaker bond compared to oxygen with higher bond orders.

The bond order gives us insights into the stability and reactivity of the different oxygen ions.

Paramagnetism

In simple terms, paramagnetism refers to the presence of unpaired electrons in an atom or a molecule which leads to its attraction to a magnetic field. When an oxygen species has unpaired electrons, it is paramagnetic. Let's see how this applies to the oxygen ions:

• \(\mathrm{O}_{2}^{+}\): This ion has 11 electrons with one unpaired electron, making it paramagnetic.
• \(\mathrm{O}_{2}^{-}\): Similar to \(\mathrm{O}_{2}^{+}\), it has an unpaired electron and is therefore paramagnetic as well.

Unpaired electrons cause these ions to be attracted to an external magnetic field. The presence of paramagnetism in a molecule indicates interesting magnetic properties that can be important in applications of physics and chemistry.

Diamagnetism

Diamagnetism, on the other hand, occurs in substances where all the electrons are paired. These substances typically exhibit repulsion from a magnetic field. It's a very subtle effect but an important distinction from paramagnetism.

• \(\mathrm{O}_{2}^{2+}\): This ion, having lost two electrons from the neutral oxygen molecule, has no unpaired electrons and is therefore diamagnetic.
• \(\mathrm{O}_{2}^{2-}\): With full filling of its molecular orbitals, \(\mathrm{O}_{2}^{2-}\) also exhibits diamagnetism as all its electrons are paired.

Diamagnetic materials are often overlooked because their magnetic response is weak compared to paramagnets, but this property is useful in some technological applications like magnetic levitation.

Oxygen Ions

Oxygen ions, with different numbers of electrons, exhibit a range of chemical and physical properties that are noteworthy under molecular orbital theory.

Different Forms of Oxygen Ions

Oxygen typically occurs as \(\mathrm{O}_2\), but it can gain or lose electrons, forming ions such as:

• \(\mathrm{O}_{2}^{2+}\): Gained by removing electrons, it is less common in nature.
• \(\mathrm{O}_{2}^{+}\): Has one less electron, making it paramagnetic.
• \(\mathrm{O}_{2}^{-}\): Acquires an extra electron and is paramagnetic as well.
• \(\mathrm{O}_{2}^{2-}\): Known as the peroxide ion, it is stable particularly under certain conditions in the liquid or gas phase.

These ions demonstrate unique characteristics based on the number and arrangement of electrons. Understanding these variations helps in the study of chemical bonding and the behavior of molecules under different circumstances.