Question

The two elements A and B have similar chemical properties and do not form solid Hydrogen carbonate but react with Nitrogen forming Nitrides.Elements A and B are:

• A. Sodium$\left(\mathrm{Na}\right)$ and Calcium$\left(\mathrm{Ca}\right)$
• B. Cesium $\left(\mathrm{Cs}\right)$ and Barium $\left(\mathrm{Ba}\right)$
• C. Sodium$\left(\mathrm{Na}\right)$ and Rubidium $\left(\mathrm{Rb}\right)$
• D. Lithium$\left(\mathrm{Li}\right)$ and Magnesium $\left(\mathrm{Mg}\right)$

Answer 1

The correct option is D

Lithium$\left(\mathrm{Li}\right)$ and Magnesium $\left(\mathrm{Mg}\right)$

Explanation for the correct options:

(D) Lithium$\left(\mathrm{Li}\right)$ and Magnesium $\left(\mathrm{Mg}\right)$

• Lithium and Magnesium do not form solid bicarbonate. When these elements react with Nitrogen they give nitrides.
• $$\begin{gathered} 6\mathrm{Li}\left(\mathrm{s}\right)+{\mathrm{N}}_2\left(\mathrm{g}\right)\stackrel{∆}{\to }2{\mathrm{Li}}_3\mathrm{N}\left(\mathrm{s}\right) \\ \left(\mathrm{Lithium}\right)\left(\mathrm{Nitrogen}\right)(\mathrm{Lithium}\mathrm{Nitride}) \end{gathered}$$
• When Lithium reacts with Nitrogen forming a white solid Lithium Nitride.
• $$\begin{gathered} 3\mathrm{Mg}\left(\mathrm{s}\right)+{\mathrm{N}}_2\left(\mathrm{g}\right)\stackrel{∆}{\to }{\mathrm{Mg}}_3{\mathrm{N}}_2\left(\mathrm{s}\right) \\ \left(\mathrm{Magnesium}\right)\left(\mathrm{Nitrogen}\right)(\mathrm{Magnesium}\mathrm{nitride}) \end{gathered}$$
• When Magnesium reacts with Nitrogen forming greenish-yellow Magnesium Nitride.
• Lithium and Magnesium are the only elements from Group I that form a stable and lattice energy that is released.
• Lithium forms liquid Hydrogen carbonate due to its size and polarising power is high.
• Lithium and Magnesium show a diagonal relationship and have the same chemical characteristics.

Explanation for the incorrect options:

A. Sodium$\left(\mathrm{Na}\right)$ and Calcium$\left(\mathrm{Ca}\right)$

• Sodium and Calcium react with Nitrogen to form Sodium Nitride$\left({\mathrm{Na}}_3\mathrm{N}\right)$ and Calcium Nitride$\left({\mathrm{Ca}}_3\mathrm{N}\right)$.
• $$\begin{gathered} 6\mathrm{Na}\left(\mathrm{s}\right)+{\mathrm{N}}_2\left(\mathrm{g}\right)\stackrel{∆}{\to }2{\mathrm{Na}}_3\mathrm{N}\left(\mathrm{s}\right) \\ \left(\mathrm{Sodium}\right)\left(\mathrm{Nitrogen}\right)(\mathrm{Sodium}\mathrm{Nitride}) \end{gathered}$$
• Sodium nitride is readily decomposed due to its instability.
• $$\begin{gathered} 3\mathrm{Ca}\left(\mathrm{s}\right)+{\mathrm{N}}_2\left(\mathrm{g}\right)\stackrel{∆}{\to }{\mathrm{Ca}}_3{\mathrm{N}}_2\left(\mathrm{s}\right) \\ \left(\mathrm{Calcium}\right)\left(\mathrm{Nitrogen}\right)(\mathrm{Calcium}\mathrm{Nitride}) \end{gathered}$$

B. Cesium $\left(\mathrm{Cs}\right)$ and Barium $\left(\mathrm{Ba}\right)$

• $$\begin{gathered} 6\mathrm{Cs}\left(\mathrm{s}\right)+{\mathrm{N}}_2\left(\mathrm{g}\right)\stackrel{∆}{\to }2{\mathrm{Cs}}_3\mathrm{N}\left(\mathrm{s}\right) \\ \left(\mathrm{Caesium}\right)\left(\mathrm{Nitrogen}\right)(\mathrm{Caesium}\mathrm{nitride}) \end{gathered}$$
• It is a highly unstable reaction so Caesium nitride cannot be formed.
• $$\begin{gathered} \mathrm{Ba}\left(\mathrm{s}\right)+{\mathrm{N}}_2\left(\mathrm{g}\right)\stackrel{∆}{\to }{\mathrm{Ba}}_3{\mathrm{N}}_2\left(\mathrm{s}\right) \\ \left(\mathrm{Barium}\right)\left(\mathrm{Nitrogen}\right)(\mathrm{Barium}\mathrm{Nitride}) \end{gathered}$$
• Barium nitride is unstable.

C. Sodium$\left(\mathrm{Na}\right)$ and Rubidium $\left(\mathrm{Rb}\right)$

• $$\begin{gathered} 6\mathrm{Rb}\left(\mathrm{s}\right)+{\mathrm{N}}_2\left(\mathrm{g}\right)\stackrel{∆}{\to }2{\mathrm{Rb}}_3\mathrm{N}\left(\mathrm{s}\right) \\ \left(\mathrm{Rubidium}\right)\left(\mathrm{Nitrogen}\right)(\mathrm{Rubidium}\mathrm{Nitride}) \end{gathered}$$
• It is highly unstable

Hence option (D) is correct, Lithium$\left(\mathrm{Li}\right)$ and Magnesium $\left(\mathrm{Mg}\right)$ have similar chemical properties and do not form solid Hydrogen carbonate but react with Nitrogen forming Nitrides.