Points of Difference between Lithium and other Alkali Metals

Lithium departs from the rest of Group 1 in a number of concrete, observable ways:

• Hardness and melting/boiling points: Lithium is distinctly harder than the other alkali metals, and its melting and boiling points are correspondingly higher.
• Reactivity and reducing power: Lithium is the least reactive of the group in a kinetic sense, yet — because of its very high hydration enthalpy — it is the strongest reducing agent of all of them. On burning in air it forms mainly the monoxide $Li_2O$ together with the nitride $Li_3N$, a combination none of the other alkali metals produces.
• Hydrate formation: $LiCl$ is deliquescent and crystallises as the hydrate $LiCl\cdot 2H_2O$; the chlorides of the other alkali metals do not form hydrates at all.
• Hydrogencarbonate: Lithium hydrogencarbonate cannot be isolated as a solid, whereas every other alkali metal forms a stable solid hydrogencarbonate.
• Reaction with ethyne: Unlike the other alkali metals, lithium does not form an ethynide (acetylide) on reaction with ethyne.
• Thermal decomposition of the nitrate: Heated lithium nitrate decomposes all the way to the oxide, releasing both $NO_2$ and $O_2$, whereas the nitrates of the other alkali metals stop at the nitrite: …