Question:

Among the alkali metals, lithium salts exhibit the least electrical conductance in aqueous solutions. Smaller the radius of the hydrated cation, lower is the electrical conductance in aqueous solutions.

Updated On: Jul 28, 2022
  • If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion
  • If both Assertion and Reason are true but the Reason is not the correct explanation of the Assertion
  • If Assertion is true but Reason is false
  • If both Assertion and Reason are false
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The Correct Option is C

Solution and Explanation

Hydration energy varies inversely with size. Hence, as we move from $Li$ to $Cs$, size of alkali metals increases and thus, hydration energy decreases. Thus, lithium ion being smallest in size among alkali metals, is most extensively hydrated and becomes largest in size. Thus, it has least electrical conductivity among alkali metals. Electrical conductance $\propto \frac{1}{\text { size of hydrated cation }}$
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Concepts Used:

Group 1 Elements

Group one of alkali metals is s-block elements with just one electron in their s-orbital. They are are alkali metals. They are named so because of the alkaline nature of the hydroxides and oxides.

Alkali metals are characterized by one s-electron in the valence shell of their atoms.

Alkali metals have a corresponding [Noble gas] ns1 electronic configuration. They occupy the first column of the periodic table. Alkali elements are:

  • Lithium(Li)
  • Sodium(Na)
  • Potassium (K)
  • Rubidium (Ru)
  • Cesium (Cs)
  • Francium (Fr)

They have occupied successive periods from first to seven. Francium is a radioactive element with very low half-life.

Electronic Configuration:

  • Alkali metals have one electron in their valence shell.
  • The electronic configuration is given by ns1. For example, the electronic configuration of lithium is given by 1ns1 2ns1.
  • They tend to lose the outer shell electron to form cations with charge +1 (monovalent ions).

This makes them the most electropositive elements and due to the same reason, they are not found in the pure state.