Problem 58 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following sets has the strongest tendency to form anions? (a) \(\mathrm{V}, \mathrm{Cr}, \mathrm{Mn}\) (b) \(\mathrm{N}, \mathrm{O}, \mathrm{F}\) (c) \(\mathrm{Ga}, \mathrm{In}, \mathrm{Tl}\) (d) \(\mathrm{Na}, \mathrm{Mg}, \mathrm{Al}\)

Step-by-Step Solution

Answer

The set \( \mathrm{N, O, F} \) has the strongest tendency to form anions.

Step 1: Recognize Element Properties

First, identify the major property linked to the tendency of elements to form anions: high electronegativity. Elements with high electronegativity have a stronger pull on electrons and, thus, a greater tendency to form anions.

Step 2: Analyze Set (a)

Consider the elements V (Vanadium), Cr (Chromium), and Mn (Manganese). These are transition metals, which typically do not have a strong tendency to form anions due to their lower electronegativity compared to nonmetals.

Step 3: Analyze Set (b)

Look at the elements N (Nitrogen), O (Oxygen), and F (Fluorine). These are nonmetals with high electronegativity values. Fluorine is the most electronegative element and has the strongest tendency to form anions, followed by oxygen and nitrogen.

Step 4: Analyze Set (c)

Review the elements Ga (Gallium), In (Indium), and Tl (Thallium). These elements are metals with relatively low electronegativity, hence they do not have a strong tendency to form anions.

Step 5: Analyze Set (d)

Check the elements Na (Sodium), Mg (Magnesium), and Al (Aluminum). These are metals with low electronegativity, especially when compared to nonmetals. They are more likely to form cations than anions.

Step 6: Compare and Decide

Compare all sets observed. Set (b) with elements N, O, and F consists of nonmetals with the highest electronegativity values, indicating a strong tendency to form anions. Therefore, set (b) is the answer.

Key Concepts

Anion Formation

Anions are negatively charged ions formed when an atom gains one or more electrons. This process is particularly favorable for elements with high electronegativity. Electronegativity refers to an atom’s ability to attract and hold onto electrons.

Elements most likely to form anions include nonmetals. Their atoms have a high affinity for electrons, enabling them to form stable anions by completing their outer electron shells.

• When nonmetals, such as fluorine, gain electrons, they fill their outer shell, achieving a more stable, noble gas electronic configuration. This process of electron gain results in anions.
• This is in contrast to metals, which generally form cations by losing electrons due to their lower electronegativity values.

Understanding anion formation is key to predicting chemical reactions and compounds involving nonmetals.

Nonmetals

Nonmetals are elements typically found on the right side of the periodic table. They possess several unique properties that distinguish them from metals.

Primarily, nonmetals have high electronegativity and ionization energy, which makes them more likely to gain electrons during chemical reactions.

• Common nonmetals that readily form anions are elements like nitrogen (N), oxygen (O), and fluorine (F). These elements have almost full outer electron shells, and need only a few additional electrons to achieve a stable form.
• This strong tendency to gain electrons results from their desire to attain a complete valence shell, similar to the stable configuration of noble gases.

The behavior of nonmetals explains many of their physical properties. For instance, they are poor conductors of heat and electricity because they do not have free electrons.

Periodic Table Trends

The periodic table is a powerful tool that helps us understand the behavior of elements, including their tendency to form anions.

A key trend to note is how electronegativity changes across the table:

• As you move from left to right across a period, electronegativity increases. This explains why elements like fluorine, close to the noble gases on the right, are highly electronegative.
• As you move down a group, electronegativity decreases. This is because additional electron shells added in each new period increase the distance between the nucleus and outermost electrons, reducing the effective nuclear charge experienced by these electrons.

These trends in electronegativity play a critical role in an element's chemical behavior. Nonmetals in the upper right part of the periodic table, such as oxygen and fluorine, show the highest tendencies to form anions due to these underlying periodic trends.