Question

Which among the following is NOT a factor in Hume-Rothery rules of formation of substitutional solid solutions

• A. crystal structure
• B. relative size
• C. chemical affinity
• D. chemical Reactivity

Hint:

Remember the four Hume-Rothery rules using the mnemonic: Size, Structure, Valency, Electronegativity (S-S-V-E).
- Size difference $< 15\%$
- Same crystal structure
- Same valency (preferably)
- Similar electronegativity (low affinity for compound formation)

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to identify which of the given options is not part of the Hume-Rothery rules that govern the solubility of solute atoms in a solvent matrix to form a substitutional solid solution.

Step 2: Detailed Explanation:

• Hume-Rothery Rules Overview:
The Hume-Rothery rules are a set of empirical guidelines that predict whether two elements will form a substitutional solid solution with high solubility. The rules are based on four primary factors:
1. Atomic Size Factor (Relative Size): The difference in atomic radii of the solute and solvent atoms should be less than $15\%$. Otherwise, the lattice strain is too large, and solubility is low.
2. Crystal Structure Factor: For complete solid solubility, the crystal structures of both elements must be identical (e.g., both FCC or both BCC).
3. Electronegativity Chemical Affinity Factor: The electronegativities of the two elements should be similar. If there is a large difference in electronegativities (high chemical affinity), the elements tend to form an intermetallic compound rather than a solid solution.
4. Relative Valency Factor: A metal will dissolve a metal of higher valency more readily than one of lower valency.

• Analysis of Options:
- "crystal structure" is a primary Hume-Rothery factor.
- "relative size" is the atomic size factor, a primary Hume-Rothery factor.
- "chemical affinity" (electronegativity difference) is a primary Hume-Rothery factor.
- "chemical Reactivity" is a broad kinetic term and is not a formal factor listed in the thermodynamic Hume-Rothery rules.

Step 3: Final Answer:
Chemical reactivity is not a factor in Hume-Rothery rules of formation of solid solutions.