Rubidium (Rb)


  • Symbol: Rb
  • Atomic Number: 37
  • Atomic Weight: 85.4678
  • Element Classification: Alkali Metal
  • Discovered By: Robert Bunsen and Gustav Kirchhoff
  • Discovery Date: 1861
  • Name Origin: Latin: ‘rubidus’ (deepest red), for the red lines in its spectrum
  • Density(g/cc): 1.532
  • Melting Point: 39.31°C
  • Boiling Point: 688°C
  • Appearance: Soft, silvery-white metallic
  • Atomic Radius(pm): 248


Rubidium was discovered in 1861 by German chemists Robert Bunsen and Gustav Kirchhoff, who were pioneers in the use of spectroscopy. They detected rubidium’s existence through its bright red spectral lines in the mineral lepidolite. The name rubidium comes from the Latin word ‘rubidus’, meaning deepest red, reflecting the color of its spectral emissions. This discovery was part of a broader exploration of elements using spectroscopic methods, showcasing the power of this technique in identifying elements based on their spectral lines.

Relation to Other Elements

Rubidium is an alkali metal, located in group 1 of the periodic table, which also includes lithium, sodium, potassium, cesium, and francium. Alkali metals are known for their single electron in the outermost shell, making them highly reactive, especially with water. Rubidium shares many physical and chemical properties with other alkali metals, such as softness, low melting points relative to most other metals, and the tendency to form +1 ions. It is more reactive than potassium but less so than cesium.

Natural Occurrence

Rubidium is the 23rd most abundant element in the Earth’s crust, found in a variety of minerals, including lepidolite, pollucite, and carnallite, but it is never found in nature in its elemental form due to its high reactivity. It is more abundant in the Earth’s crust than zinc or copper. Rubidium isotopes are also found in trace amounts in the human body, where they have no known biological role.


Rubidium has several specialized uses:

  • Research and Development: Rubidium and its compounds are used in research, particularly in chemical and physical experiments involving alkali metals.
  • Electronics: Rubidium vapor is used in atomic clocks, where it serves as a frequency standard to maintain accuracy in global positioning systems (GPS) and other telecommunications applications.
  • Medical Imaging: The radioactive isotope rubidium-82 is used in positron emission tomography (PET) scans, particularly in cardiac imaging to assess blood flow and diagnose heart conditions.
  • Specialized Glasses: Rubidium can be used in making special glasses and ceramics, where it enhances certain properties like optical quality or electrical conductivity.

Rubidium’s discovery via spectroscopy opened up new avenues for identifying elements and studying their properties. While not as widely used as some other elements due to its reactivity and rarity, rubidium’s applications in science and technology demonstrate the importance of even the less common elements in advancing knowledge and technological capabilities.

Krypton (Kr)

Strontium (Sr)