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I have read that the trend for conductivity in groups 1 and 2 is a decrease down the groups (generally). Apparently this is because the atoms of each element get larger, so while the number of electrons per atom stays the same, the number of electrons per unit volume decreases. But the amount of shielding between the outer electrons and the nucleus increases, so surely the outer electrons become easier to donate to the delocalised sea, and will experience less attraction to the positive ions around them. Which I would have thought made them more mobile and therefore made the metal a better conductor. Obviously I'm wrong but can someone please explain why?

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  • $\begingroup$ The conductivity of metals depends quite fundamentally upon the temperature at which it is measured - and without clarifying what temperature(s) you are interested in this question is difficult to answer. You probably mean low temperatures as you are ignoring the contribution to the resistivity from lattice vibrations, but now I am guessing. $\endgroup$
    – Ian Bush
    Commented Mar 15, 2022 at 21:27

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the alkali metal ions in aqueous solution have high electrical conductance. the electrical conductance of Li+ ions expected to be highest, which is smallest ions in size, as ionic size increases down the group.

               however, we find experimently that electric conductance increases down the group and Cs+ has the highest conductance while Li+ has lowest.

this is evidently the reverse of what we expect. This anomaly arises from the fact that alkali metal ions are hydrated to diffrent extents.The Li+ ion is hydrated to the maximum extent due to its high charge/size ratio compared to other alkali metals the extent of hydration decrease down the group, thus Cs+ is least hydrated Li+ ion due to high hydration is the biggest while Cs+ ion due to smaller hydration is the smallest. thus, the ionic size in aqueous solutions, instead of increasing actually decreases on moving from Li+ to Cs+ as a result of which ionic mobility increases as we move from Li+ to Cs+. Hence, the ionic conductance, instead of decreasing, actually increases on moving from Li+ to Cs+

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    $\begingroup$ The question is about the elemental metals, not the ions in (aqueous) solution $\endgroup$
    – Ian Bush
    Commented Apr 13, 2023 at 7:12

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