Problem 79 - A Complete Resource Book in Chemistry for JEE Main

Question

An element (A) occurs in a short period having the configuration \(\mathrm{ns}^{2} \mathrm{np}^{1}\). The formula and nature of its oxide is (a) \(\mathrm{AO}_{3}\), acidic (b) \(\mathrm{A}_{2} \mathrm{O}_{3}\), amphoteric (c) \(\mathrm{AO}_{3}\), basic (d) \(\mathrm{A}_{2} \mathrm{O}_{3}\), basic

Step-by-Step Solution

Answer

The correct formula and nature of the oxide is (b) \( \mathrm{A}_{2} \mathrm{O}_{3} \), amphoteric.

Step 1: Determine the Element's Group

The electronic configuration given is \( \mathrm{ns}^{2} \mathrm{np}^{1} \), which corresponds to group 13 (III A) of the periodic table. Elements in this group include boron, aluminum, gallium, etc.

Step 2: Identify the Element in a Short Period

Since the short periods are periods 2 and 3, and group 13 elements in those periods are boron and aluminum, the element could be boron or aluminum.

Step 3: Analyze Oxide Formation

Group 13 elements typically form oxides in the form of \( \mathrm{A}_{2}\mathrm{O}_{3} \). Thus, we have either \( \mathrm{B}_{2}\mathrm{O}_{3} \) or \( \mathrm{Al}_{2} \mathrm{O}_{3} \).

Step 4: Consider the Nature of Oxide

In general, boron oxides are acidic, while aluminum oxides are amphoteric. Given the options and configurations, one matches this amphoteric characteristic.

Step 5: Match the Provided Options

Option (b) \( \mathrm{A}_{2} \mathrm{O}_{3} \), amphoteric, correctly describes \( \mathrm{Al}_{2} \mathrm{O}_{3} \). Boron would form \( \mathrm{B}_{2} \mathrm{O}_{3} \) which is acidic. Aluminum matches the amphoteric nature.

Key Concepts

Group 13 Elements

The periodic table's Group 13 is an intriguing column that includes elements like boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl). These elements are sometimes referred to as the "ico-group," derived from the ancient Greek word 'eikos,' meaning 20, since this group starts from aluminum with an atomic number slightly greater than 20. Members of Group 13 are characterized by their electronic configuration, \( \text{ns}^{2} \text{np}^{1} \), which means they have three electrons in their outermost shell.
This electron configuration is crucial because it indicates the trivalency of these elements, giving them specific chemical properties.
As we move down the group from boron to thallium, we notice a shift from non-metallic to metallic characteristics.

• Boron is a metalloid exhibiting non-metal characteristics.
• Aluminum is a light metal widely used in the aerospace industry.
• Gallium, indium, and thallium are metals with increasing density and metallic traits.

It's important to recognize that the reactivity and bonding tendencies of these elements are strongly influenced by this group configuration.

Oxide Formation

Oxide formation among Group 13 elements is an interesting process reflecting their unusual electron configurations. Typically, these elements tend to form oxides with the formula \(\mathrm{A}_{2}\mathrm{O}_{3}\), where 'A' stands for the group element.
In a chemical reaction, these elements lose their three outermost electrons and form trivalent oxides. However, not all members of Group 13 form oxides in exactly the same way or with identical properties.
For instance,

• Boron forms \(\mathrm{B}_{2}\mathrm{O}_{3} \), an acidic oxide.
• Aluminum forms \(\mathrm{Al}_{2}\mathrm{O}_{3} \), a classic amphoteric oxide.

The trend typically shows variations in oxide properties from acidic for boron to amphoteric for aluminum. As you go down the group, the oxides generally become more basic, reflecting the increasing metallic nature of these elements.

Amphoteric Nature

The term "amphoteric" describes substances that can behave as both acids and bases.
When it comes to oxides, this means that depending on the surrounding environment and reacting substances, these oxides can either donate or accept protons (H\(^+\) ions).
Aluminum oxide (\(\mathrm{Al}_{2}\mathrm{O}_{3} \)) is a well-known amphoteric substance.

• In acidic environments, it acts as a base, reacting with the acid to form salts and water.
• Conversely, in basic environments, it acts as an acid, neutralizing the base to again form salts and water.

This dual nature makes amphoteric oxides like \(\mathrm{Al}_{2}\mathrm{O}_{3} \) versatile in various chemical reactions and industrial applications.
Understanding amphoteric characteristics is essential, especially when dealing with reactions involving different pH levels.

Periodic Table

The periodic table is a fundamental tool in the field of chemistry. It is an organized arrangement of all known elements in order of increasing atomic number. This table not only categorizes elements by their properties but also illustrates how these properties change across periods (rows) and groups (columns).
The table's design allows for a quick assessment of an element's characteristics based on its position. Each element in the periodic table has a unique electronic configuration, which gives insight into its chemical behavior.

• For example, Group 13, where elements have \(\text{ns}^{2}\text{np}^{1} \) configurations, shares similarities and trends in their chemical activity.
• Moving across a period, we see a progression from metallic to non-metallic characteristics.
• Down a group, however, elements typically become more metallic in nature.

Understanding the periodic table is thus essential for predicting the reactivity and properties of elements, making it an indispensable guide for scientists and students alike.