Lithium.

Chemical composition

The main physical properties of lithium:

Relative elongation, % 50-70

Lithium refers to metals for which the manufacture of a sample with a clean, unoxidized surface is quite a challenge. The problem is its high reactivity. If you throw pieces of lithium and sodium into the water, sodium will react with water much faster. If you take a large enough chunk of sodium (more frame), it is likely to melt, light up, and there will be a small explosion of released hydrogen. Lithium reacts with water much calmer (may be slightly faster than calcium), but at elevated temperatures, lithium begins to show much greater activity. It corrodes most materials, dissolves metals, corrodes almost all types of glass, burns in nitrogen. It cannot be distilled in a vacuum into an ampoule, like other alkali metals, since molten lithium instantly corrodes the glass installation. By the way, it reacts with nitrogen at room temperature, so my attempt to cut off a piece of lithium in a nitrogen box was unsuccessful: lithium instantly covered with a black coating (most likely nitride). In most collections of elements, a sample of lithium is under a layer of mineral oil (however, there it darkens).