Question:

When alkaline earth metals dissolve in ammonia, they form coloured solution like alkali metals. Which of the following observations regarding the reaction are correct ? (i) Dilute solutions are bright blue in colour due to solvated electrons. (ii) These solutions decompose to form amides and hydrogen. (iii) From this solution the ammoniates $[M(NH_3)_6]^{2+}$ can be recovered by evaporation.

Updated On: Jul 7, 2022
  • Only (i) and (ii)
  • Only (i), (ii) and (iii)
  • Only (ii) and (iii)
  • Only (i)
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The Correct Option is B

Solution and Explanation

All the observations are correct. $M \to M^{3+} +2e^-$ $2NH_3+2e^- \to 2NH^-_2 +H_2$ $M^{2+}+2NH^-_2 \to M(NH_2)_2 {->[{\text{eyporation}}]} [M(NH_3)_6]^{2+}$ $[M(NH_3)_6]^{2+} \to M(NH_2)_2 + 4NH_3 + H_2$
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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.