Rubidium

Rubidium (chemical symbol - Rb, from Lat. Rubidium) is a chemical element of the 1st group (according to the outdated classification - the first group of the main subgroup, IA), the fifth period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 37.

The simple substance rubidium is a soft, low-melting alkali metal of silvery-white color[4].

Metallic rubidium has similarities with metallic potassium and metallic caesium in appearance, softness and conductivity[5]. Rubidium should not be stored outdoors, as a reaction will occur with the release of a large amount of heat, sometimes even leading to ignition of the metal[6]. Rubidium is the first alkali metal in the group whose density is higher than that of water, so it sinks, unlike the metals above it in the group.