Theoretical Basis of Hardness and Softness
Why [CoF6]-3 is more stable than [CoI6]-3 explain it by HSAB principle ?
In [CoF6]-3 and [CoI6]-3 complexes, cobalt is in +3 oxidation state and act as a hard acid. Fluoride ion is a hard base and iodide ion is a soft base according to HSAB principle. Therefore, in [CoF6]-3, the hard acid (Co+3) and hard base (F−) form a stable complex than the [CoI6]-3 form by a hard acid (Co+3) and soft base (I−).Why does CsF react with LiI to give CsI and LiF ?
The reaction between LiI and CsF to give LiF and CsI always proceeds to give LiF and CsI because the combination of Soft-Soft and Hard-Hard species is a stable molecule.Li+ is hard acid, I− is a weak base, Cs+ is soft acid and F− is hard base. So, the combination of Li+ and F− gives a stable molecule LiF. Similarly, the combination of Cs+ and I− gives a stable molecule CsI.
LiI(Hard-soft) + CsF(soft-hard) → LiF(Hard-hard) + CsI(Soft-soft)
Why is AgI(s) water-insoluble, but LiI water-soluble ?
AgI is a soft acid-soft base combination, while LiI is hard-soft. The interaction between Li+ and I- ions is not strong. Therefore, AgI(s) water-insoluble, but LiI water-soluble.Why does strong Lewis acid-strong Lewis base interactions prevail over hard-soft acid-base interactions ?
When the HOMO of the Lewis base and the LUMO of the Lewis acid are similar in energy, the bonding molecular orbitals produced are significantly lower in energy and thus, electron occupation of these bonding MOs give rise to significant stabilisation. This occurs when hard Lewis acids and hard Lewis bases react and also when soft Lewis acids and soft Lewis bases react. This is the molecular orbital basis of Pearson's Hard Soft Acid Base Principle.AgI2- is stable but AgF2- does not Why ?
AgI2- is formed by soft- soft combination while AgF2- is formed by soft –hard combination. So, accoding to the HSAB principle, AgI2- will be more stable than AgF2-.IMPORTANT QUESTIONS 1. Define soft base and give one example. 2. What is symbiosis? 3. How does HSAB principle govern the occurrence of minerals? 4. Define absolute hardness. 5. Give two examples of border line acids. 6. Which of the following is odd among the following: Li+ , Ga3+, Cd2+, K+
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