Chemistry - PERIODIC TABLE Question with Solution | TestHub
In a series of compounds , and MI , the melting point decreases as . However, for another metal , the trend is reversed for and . Which of the following factors is most likely responsible for this reversal?
Options:
Answer:
Solution:
Concept: Born-Landé equation, Lattice Energy vs. Polarization competition.
Solution:
1. Standard Trend: Usually, melting point decreases down the halogen group because Lattice Energy decreases ().
2. The Reversal: If M′ is a very small, highly polarizing cation (like Li⁺ or Be²⁺), the polarization of larger anions (Cl⁻, Br⁻, I⁻) becomes so extreme that the compound's character shifts from ionic to covalent.
3. Result: M′F remains highly ionic (high MP), but M′I becomes covalent (low MP). The question asks why the trend might reverse or deviate—this is due to the covalent contribution overriding the lattice energy trend.
Final Answer: Option (D)