Problem 89 - A Complete Resource Book in Chemistry for JEE Main

Question

\(\mathrm{TiO}_{2}\) (rutile) shows \(6: 3\) coordination. The solid having rutile like structure among the following is (a) \(\mathrm{KCl}\) (b) \(\mathrm{SnO}_{2}\) (c) \(\mathrm{ZnS}\) (d) none of these

Step-by-Step Solution

Answer

The solid with a rutile-like structure is (b) \(\mathrm{SnO}_{2}\).

Step 1: Understand the Coordination Number

Rutile structure is known for having a coordination number of 6 for the cation and 3 for the anion. This means the metal cations are surrounded by 6 anions, and each anion is surrounded by 3 cations.

Step 2: Analyze Each Option

We need to determine which compound has a rutile-like structure. (a) KCl: KCl typically crystallizes in a rock-salt structure with 6:6 coordination. (b) SnO₂: SnO₂ is known to crystallize in a rutile structure with 6:3 coordination. (c) ZnS: ZnS typically crystallizes in a zinc blende or wurtzite structure with 4:4 coordination. (d) None of these: "None of these" applies only if none of the above options match, but SnO₂ does.

Step 3: Identify the Correct Answer

Based on the coordination numbers explained, option (b) mathrm{SnO}_{2} matches the rutile-like structure with 6:3 coordination. This makes it the correct answer.

Key Concepts

Coordination Numbers

In solid state chemistry, the concept of coordination numbers (CN) is fundamental. This number indicates how many ions of opposite charge surround a given ion. The coordination number typically varies depending on factors such as atomic size and ionic charge. It plays a critical role in determining the geometry and structure of the crystal lattice.

The rutile structure, which is a variant of titanium dioxide (\( ext{TiO}_2 \)), is characterized by a unique coordination number configuration: 6 for the cation and 3 for the anion. This means each titanium cation (metal cation) is surrounded by six oxygen anions, whereas each oxygen anion is surrounded by three titanium cations. Understanding this geometric arrangement helps predict the properties of the material, such as stability and density. The coordination number can significantly influence the properties and types of bonds present in any crystal structure.

Tin(IV) Oxide (SnO2)

Tin(IV) oxide, also known as stannic oxide, is an interesting compound in the field of solid state chemistry. Its chemical formula is \( ext{SnO}_2 \) and it's known to crystallize in a rutile structure, similar to \( ext{TiO}_2 \).

This material exhibits a coordination number of 6:3, where each tin cation is coordinated by six oxygen anions, and each oxygen anion is in turn coordinated by three tin cations. Such coordination gives \( ext{SnO}_2 \) its unique properties of being a semiconductor with high transparency for visible light.

Due to its properties, \( ext{SnO}_2 \) is widely used in various applications, such as gas sensors, transparent conducting films, and as a catalyst in chemical reactions. Its rutile structure contributes to its stability and functionality in these applications.

Solid State Chemistry

Solid state chemistry focuses on the synthesis, structure, and properties of solid phase materials, with emphasis on how atoms are arranged and how this arrangement affects the overall properties of the material.

At the heart of solid state chemistry is the understanding of how various structures form from different combinations of elements under various environmental conditions. The principles behind this study are crucial in the development of new materials with specific desired properties.

A key concern in solid state chemistry is rationalizing why certain crystals adopt particular structures, like the rutile structure for some metal oxides. When analyzing these structures, factors such as atomic radius, electronic configurations, and thermodynamics are considered. Knowing and understanding these details allows scientists to engineer solids with valuable and unique characteristics.

Crystal Structures

Crystal structures are vast and varied, describing how atoms, ions, or molecules are spatially arranged in a crystal. Each crystal structure is defined by its unit cell, which is the smallest repeating unit that reflects the whole crystal’s symmetry.

The rutile structure, which is characteristic of certain metal oxides like \( ext{TiO}_2 \) and \( ext{SnO}_2 \), has a tetragonal unit cell. In this structure, each metal ion is octahedrally coordinated by six oxygen ions, forming a rod-like structure throughout the crystal.

This crystal structure not only dictates how tightly packed the ions are but also affects important physical properties such as melting point, density, and electronic bandwidth. Understanding these structures is essential for explaining and predicting material properties, as well as manipulating them to develop new materials with enhanced or novel characteristics.