Explain the behavior of alkali metals in liquid ammonia and comment on their colour and magnetism on being left standing?

When alkali metals such as lithium, sodium, and potassium are placed in liquid ammonia, they dissolve and form a deep blue solution. This is due to the formation of solvated electrons, which are responsible for the blue color. The solvated electrons are formed when the alkali metal atoms lose an electron to the ammonia molecules, creating a negatively charged species.

When left standing, the color of the solution may change over time. For example, the blue color of the solution containing lithium may fade to a yellowish color, while the solution containing sodium may turn orange. This change in color is due to the formation of different solvated electron species as the metal atoms react with the ammonia.

In terms of magnetism, the solutions of alkali metals in liquid ammonia are paramagnetic, meaning they are weakly attracted to a magnetic field. This is because the solvated electrons have unpaired spins, which align with an external magnetic field. However, the paramagnetism of the solutions is relatively weak compared to other magnetic materials.

Overall, the behavior of alkali metals in liquid ammonia is characterized by the formation of solvated electrons, which give the solutions their distinctive color and paramagnetic properties.