Problem 49 - A Complete Resource Book in Chemistry for JEE Main

Question

The correct order of electronegativity for \(\mathrm{O}, \mathrm{O}^{+}\)and \(\mathrm{O}^{-}\)is (a) \(\mathrm{O}^{-}>\mathrm{O}>\mathrm{O}^{+}\) (b) \(\mathrm{O}>\mathrm{O}^{+}>\mathrm{O}^{-}\) (c) \(\mathrm{O}^{+}>\mathrm{O}^{-}>\mathrm{O}\) (d) \(\mathrm{O}^{+}>\mathrm{O}>\mathrm{O}^{-}\)

Step-by-Step Solution

Answer

The correct order is (d) \( \text{O}^{+} > \text{O} > \text{O}^{-} \).

Step 1: Understanding Electronegativity

Electronegativity is a measure of the tendency of an atom to attract a pair of electrons towards itself. It typically decreases with the addition of negative charge and increases with the addition of positive charge.

Step 2: Evaluating the Effect of Charges

Atoms with a positive charge often have higher electronegativity than their neutral counterparts, because there is a stronger attraction between the nucleus and electrons. Conversely, atoms with a negative charge have more electron-electron repulsion, making it harder to attract additional electrons.

Step 3: Arrange Based on Charge Effect

Considering the principles of electronegativity, we have: 1. \( \text{O}^{+} \) has a higher electronegativity than neutral \( \text{O} \) as it has a positive charge 2. \( \text{O} \) is naturally more capable of attracting electrons than \( \text{O}^{-} \), which already has one excess electron that causes repulsion.

Step 4: Confirm the Order

From Step 3, we deduce that electronegativity decreases in the order: \( \text{O}^{+} > \text{O} > \text{O}^{-} \). This matches option (d).

Key Concepts

Effects of Charge on Electronegativity

The effect of an atom's charge on its electronegativity is significant. Electronegativity is a measure of how strongly an atom can attract or hold onto electrons. By changing the charge, you alter the balance of forces around the atom. When an atom gains a positive charge, it means it has lost electrons. This results in a smaller electron cloud and an increased net positive pull from the protons in the nucleus toward any available electrons. As a result, the electronegativity of positively charged ions, like \( \text{O}^{+} \), is typically higher because the desire to pull electrons in increases.
Conversely, when an atom gains a negative charge, it means it has added electrons, expanding the electron cloud. This results in increased electron-electron repulsion. The more electrons there are crowding around the atom, the less effective the nuclear pull becomes in attracting additional electrons. Therefore, negatively charged ions, such as \( \text{O}^{-} \), generally exhibit lower electronegativity.
To summarize, remember these points:

• Positive charge increases electronegativity due to stronger nuclear attraction.
• Negative charge decreases electronegativity due to more electron-electron repulsion.

Electronegativity Trends

Understanding electronegativity trends helps predict how elements interact in chemical reactions. Generally, across a period in the periodic table, electronegativity increases from left to right. This is due to increasing nuclear charge and a stable electron shield that doesn't expand much, enhancing the nucleus's ability to attract electrons. Down a group, electronegativity decreases because, although the nuclear charge increases, the additional electron shells mean electrons are farther from the nucleus. This increased distance weakens the pull.
It's important to note that the specific trend for charged ions deviates because adding or removing electrons affects how strongly an atom attracts additional electrons.

• In atoms same species like \( \text{O}, \text{O}^{+}, \text{O}^{-} \):
  • A positively charged ion (like \( \text{O}^{+} \)) is more electronegative than its neutral counterpart.
  • A neutral atom (\(\text{O}\)) is more competitive for electrons compared to a negatively charged ion (\(\text{O}^{-}\)).

Chemical Bonding in Ions

In ions, the type of charge an atom possesses significantly influences its role in chemical bonding. Electronegativity plays a crucial part in ionic and covalent bonds. With ionic bonds, electrons are transferred between atoms, typically from a less electronegative atom to a more electronegative one. For instance, in a bond involving \( \text{O}^{+} \), its elevated electronegativity means it attracts electrons strongly. This could help it act as an electron acceptor in chemical reactions, forming ionic bonds.
In covalent bonds, where atoms share electrons, selecting partners involves considering electronegativity differences. A charged ion like \( \text{O}^{+} \) might attract shared electrons more effectively than rivals. Conversely, \( \text{O}^{-} \) might face challenges in competing for electrons due to its lower electronegativity.
Key takeaways for chemical bonding with ions:

• High electronegativity ions are strong candidates for electron acceptors.
• Ions with low electronegativity have less pulling power in both ionic and covalent bonding scenarios.