rubidium

Rubidium is a chemical element with the symbol Rb and atomic number 37. It is a soft, silvery‑white alkali metal in group 1 of the periodic table. Rubidium is highly reactive and is one of the first metals to tarnish in air; it is typically stored under oil or in an inert atmosphere to prevent contact with moisture and oxygen. Its melting point is 39.3 degrees Celsius, making it one of the few elements that can be melted near room temperature, and it has a relatively low density.

In chemistry, rubidium forms a range of compounds, including rubidium oxide (Rb2O), rubidium hydroxide (RbOH), and rubidium halides such as rubidium chloride (RbCl). It reacts vigorously with water to produce rubidium hydroxide and hydrogen gas. The metal is usually obtained from mineral deposits and brines; industrial production involves the reduction or electrolysis of rubidium-containing salts.

Natural rubidium consists of two isotopes, 85Rb and 87Rb, with 87Rb being radioactive and having a long half-life (about 4.9 × 10^10 years). The natural isotopic abundances are roughly 72% for 85Rb and 28% for 87Rb. Because 87Rb decays to 87Sr, rubidium‑strontium dating is used in geology to estimate the age of rocks and minerals.

Rubidium has applications in research and technology, including its use in certain atomic clocks (rubidium frequency standards) and in spectroscopy. It also appeared in early photoelectric devices and continues to be used in specialized scientific instrumentation. In common practice, rubidium is handled with care due to its high reactivity and is not considered essential for biological processes.