8.
Explanation
The chemistry of alkali metals (such as lithium, sodium, potassium, etc.) in liquid ammonia (NH3) is a fascinating area of study that involves unique reactions and properties. When alkali metals are placed in liquid ammonia, they exhibit some remarkable characteristics:
1. Dissolution of Alkali Metals: Alkali metals readily dissolve in liquid ammonia to form intensely colored solutions. This dissolution process involves the formation of solvated electrons, which are responsible for the characteristic deep blue color of the solution. For example, when sodium is added to liquid ammonia, it forms solvated electrons and sodium cations.
2. Solvated Electrons: In liquid ammonia, alkali metals lose their outermost electrons to the solvent (ammonia). These electrons are solvated, which means they are surrounded by a shell of ammonia molecules. These solvated electrons are highly reactive and are responsible for many
of the unique chemical reactions that occur in this medium.
Formation of Amides: Alkali metals in liquid ammonia can react with ammonia molecules to form metal amides. For example, with sodium, you get sodium amide (NaNH2).
The formation of amides is a result of the solvated electrons acting as strong reducing agents.
3. Reduction Reactions: Alkali metals in liquid ammonia can be used to reduce various compounds. For example, they can reduce unsaturated hydrocarbons (alkenes and alkynes), which undergo addition reactions.
4. Formation of Solvated Cations: In addition to solvated electrons, alkali metals in liquid ammonia can also form solvated cations. These cations are stabilized by the ammonia molecules and can undergo various reactions.
5. Lithium-Ammonia Compounds: Lithium, in particular, forms stable compounds with ammonia, such as lithium amide (LiNH2) and lithium imide (Li2NH). These compounds are important in organic synthesis and are used in the preparation of reducing agents.
6. High Reaction Rates: Reactions of alkali metals in liquid ammonia are known for their high reaction rates. This is partly due to the high solubility of alkali metals in ammonia and the presence of solvated electrons.
It’s important to note that the use of alkali metals in liquid ammonia requires careful handling because of the highly reactive nature of the resulting solutions. Safety precautions must be taken to prevent unintended reactions or hazards. The unique chemistry of alkali metals in liquid ammonia has
applications in organic synthesis, inorganic chemistry, and materials science.