Question

Which among the following is likely to have Schottky defect? (a) \(\mathrm{ZnS}\) (b) \(\mathrm{AgBr}\) (c) \(\mathrm{NaCl}\) (d) none of these

Short answer

Both NaCl and AgBr can have Schottky defects, but NaCl is more typically associated with them.

Step-by-step solution

Understand Schottky Defect

Schottky defect occurs in ionic crystals where an equal number of cations and anions are missing from their lattice sites to maintain electrical neutrality. This defect is typically found in ionic compounds with high coordination numbers and similar sizes of cations and anions.

Analyze Given Compounds

Examine the chemical composition of each compound to determine which could exhibit Schottky defects. Consider the types of ions, their coordination numbers, and the size differences between the cations and anions.

Evaluate 2nS

2nS is made up of b^2+n^2+ and 8- ions. It is more likely to show Frenkel defect due to the significant difference in ion sizes. Thus, rS doesn't typically show Schottky defects.

Evaluate 8gBr

8gBr can exhibit both Frenkel and Schottky defects. The similar sizes and close packing arrangement allow it to typically exhibit Schottky defects in addition to Frenkel defects.

Evaluate 8aCl

NaCl is a classic example of a compound that shows Schottky defects due to the similar size and ionic nature of Na+ and Cl- ions, and its high coordination number.

Conclusion

Considering the properties of the defects and the nature of each compound, both NaCl and AgBr can show Schottky defects, but NaCl is more classically known for it.

Key concepts

Ionic Crystals

Ionic crystals are a fascinating type of solid material. They are structures formed by the regular, repeating arrangement of ions. In these crystals, positive and negative ions are held together by strong electrostatic forces, which act in all directions to create a stable lattice. This ordered arrangement contributes to the hardness and high melting points of ionic crystals.

One remarkable characteristic is their brittleness, which means they can easily break along certain lines with a sharp edge. This happens because when pressure is applied, similar charges can be pushed together, causing a repulsion that results in a crack.

• Ionic crystals are typically found in substances like sodium chloride (common salt) and calcium fluoride.
• They exhibit distinct properties such as being poor conductors of electricity in their solid state, but better conductors when melted or dissolved in water.
• This is because the ions in the liquid state or solution can move freely, carrying an electric current.

Lattice Sites

Lattice sites refer to the fixed positions within a crystal's structure where the component ions or atoms are situated. In simple terms, think of lattice sites as parking spaces in a highly organized parking lot, where each ion has its designated spot. The arrangement and occupancy of these sites are crucial to the solid’s properties.

In ionic crystals, the precise arrangement of ions at these sites results in a repeating pattern known as a crystal lattice. This repetition contributes significantly to the crystal's physical and chemical attributes.

• Missing ions from lattice sites can cause defects like Schottky or Frenkel defects, which alter some properties of the material.
• Schottky defects involve ions vacating their lattice sites in pairs, maintaining electrical neutrality.
• Such vacancies can affect the density and other characteristics of the crystal.

Coordination Number

The coordination number is a critical concept in understanding the structure of ionic crystals. It describes the number of nearest-neighbor ions surrounding a particular ion in the crystal lattice. Imagine each ion is surrounded by other ions like a tiny, symmetrical crowd.

The coordination number is determined by factors such as the size of the ions and the type of bonding. Higher coordination numbers are often seen in compounds where the cations and anions are of similar sizes and can pack closely.

• A higher coordination number often leads to more stable structures with higher melting points.
• NaCl, for instance, has a coordination number of 6, meaning each Na+ ion is surrounded by 6 Cl- ions, and vice versa.
• The coordination number is crucial in predicting the types of defects that can occur in a crystal.

Ionic Compounds

Ionic compounds are formed from the electronegative and electropositive atoms transferring electrons to achieve stable electron configurations. This transfer results in a compound composed of charged ions. The resulting electrostatic attractions between oppositely charged ions hold the compound together.

These compounds are vital due to their diverse applications ranging from everyday table salt to critical industrial materials. Here are a few characteristics to consider:

• They usually form crystalline solids at room temperature.
• Many ionic compounds dissolve in water, where they can conduct electricity due to the free movement of ions.
• The strength of ionic bonds can significantly affect the melting and boiling points of these compounds.

Understanding their properties helps in various fields such as chemistry, material science, and engineering. Recognizing how ions interact and are affected by defects such as Schottky defect is crucial in comprehending their behavior in different scenarios.