The textbook says,

The smaller the effective size of the ion after solvation, the greater will be its conducting power."

But, on the Internet, it is explained as follows:

Radius decreases, smaller ions carrying current in small area, more associations with anions & due to this, the ions become heavy & they move with reduced speed as compared to less associated ones, & thus conductivity decreases.

The explanation is different to the what the book says. Could someone please explain this?


3 Answers 3


Small and/or highly charged ions tend to be highly solvated in water. These solvated ions may still be smaller than the solvated ions of larger ions.

However, water molecules are not as free as the molecules of a gas. Water has a much higher viscosity, for instance. So think of water as a loose gel. A large (unsolvated, or poorly solvated) ion has an easier time slipping between gaps in this gel. A smaller, more highly solvated ion is, by definition, more tightly bound to the gel network, and moves more sluggishly, as if it has to carry more of the network with it. This approach is more explanatory than predictive (see figure).

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There are lots of numbers, some agree, some disagree with any simple explanation. But a clean example is sodium vs potassium: sodium bare ion is smaller than potassium bare ion, but their hydrated ions reverse that (hydrated potassium ion is smaller than hydrated sodium ion - and check out lithium!). So potassium has a greater conductivity, for the same number of ions.


The thing can be explained as: whenever a small sized ion(particularly it's actual ionic size but not after solvation) is solvated it's effective radius increases and hence due to the increased size of the ion the space required for each ion is now lesser than what it had earlier. Hence, it can be said so conducting power changes inversely with the effective radius after solvation( as more solvated ion conducts less as compared to the less solvated).

And according to your writing both the references are correct as internet said about "conductivity and not about conducting power". So don't get confused between them.


Smaller ions get much more solvated in solvent than larger ions. Therefore with the solvent molecules by its perimeter the effective solvodynamic radius of the smaller ion increases.So now after greater solvation smaller ions get slower than the larger ions in that solvent.And hence conduction of smaller ion decreases in that solvent.


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