Structure
Not a diagram of dots on rings — a Monte-Carlo sample of the actual probability density |ψ|² for each occupied subshell. Drag to rotate. Blue and violet mark opposite signs of the wavefunction, which is what makes bonding possible.
Measured values
Every bar shows where rubidium sits among all 118 elements for that property.
Sources: IUPAC 2021 standard atomic weights · CRC Handbook of Chemistry and Physics · NIST. Values marked ~ are predicted rather than measured.
Size, to scale
Radius 248 pm — that is 0.248 nm, so about 2016 million of them side by side would span a millimetre.
Thermal range
Rubidium is liquid over a 649 K window, from 312 K to 961 K.
The story
Rubidium is the explosive alkali metal that ignites spontaneously in air and burns with a spectacular violet flame. This soft, silvery-white metal is so reactive that it must be stored under oil or inert gas to prevent violent reactions with moisture and oxygen. Named after the Latin word "rubidus" meaning deep red, rubidium produces one of the most beautiful flame colors in the periodic table. Discovered in 1861 by German chemists Robert Bunsen and Gustav Kirchhoff using their newly invented spectroscope, rubidium was the first element discovered through spectroscopy. They were analyzing the mineral lepidolite when they noticed mysterious red spectral lines that didn't match any known element. This discovery proved that spectroscopy could reveal elements present in tiny quantities, revolutionizing analytical chemistry. What makes rubidium absolutely extraordinary is its extreme reactivity. It's even more reactive than potassium and sodium, igniting instantly when exposed to air and exploding violently when dropped in water. The reaction is so energetic that it can shatter glass containers. This makes rubidium fascinating to study but dangerous to handle - it requires specialized techniques and equipment. Rubidium has some remarkable modern applications in cutting-edge technology. Rubidium atomic clocks are among the most precise timekeeping devices ever created, losing only one second every 100,000 years. GPS satellites rely on rubidium clocks to maintain the incredible precision needed for accurate positioning. These clocks work by measuring the vibrations of rubidium atoms, which oscillate at exactly 6,834,682,610.904324 times per second. Here's something incredible: rubidium is being used to create the coldest temperatures ever achieved - just billionths of a degree above absolute zero. At these ultra-low temperatures, rubidium atoms form exotic states of matter called Bose-Einstein condensates, where atoms behave more like waves than particles.
Rubidium was discovered in 1861 by German chemists Robert Wilhelm Bunsen and Gustav Robert Kirchhoff using the newly developed technique of spectroscopy, marking one of the first elemental discoveries made through spectral analysis rather than traditional chemical methods. The discovery occurred while the two scientists were analyzing mineral water from the springs at Dürkheim, Germany, using their significant spectroscope, an instrument they had developed to study the characteristic light emitted by different elements when heated. During their analysis, Bunsen and Kirchhoff observed two prominent red spectral lines that did not correspond to any known element, indicating the presence of a previously unknown substance. The distinctive deep red color of these spectral lines inspired the name "rubidium," derived from the Latin word "rubidus," meaning "deep red" or "dark red." The discovery of rubidium was particularly significant because it demonstrated the power of spectroscopy as a tool for chemical analysis and elemental discovery. Bunsen and Kirchhoff's work with rubidium came just months after their discovery of cesium using the same spectroscopic techniques, establishing them as pioneers in the field of spectroscopic analysis. The isolation of metallic rubidium proved challenging due to its extreme reactivity, and it was not until several years later that small quantities of the pure metal were obtained through electrolysis of rubidium compounds. The discovery process involved extensive chemical analysis to separate rubidium compounds from the complex mixture of salts present in the mineral water, requiring innovative separation techniques. Bunsen and Kirchhoff's methodical approach to characterizing rubidium's properties laid the groundwork for understanding alkali metal chemistry and the periodic relationships between elements. Their discovery of rubidium, along with cesium, provided crucial evidence for the developing understanding of atomic structure and the periodic classification of elements, contributing significantly to the advancement of chemical science in the 19th century.
Applications
Rubidium has found specialized applications in various high-technology fields, particularly in atomic physics research, precision timing systems, and advanced optical devices. The element's most significant application is in atomic clocks, where rubidium vapor serves as the frequency standard for highly precise timekeeping systems used in GPS satellites, telecommunications networks, and scientific research. These rubidium atomic clocks provide accuracy levels essential for global positioning systems and synchronization of communication networks worldwide. The electronics industry utilizes rubidium in specialized vacuum tubes and photocells, where the element's unique photoelectric properties make it valuable for light detection and measurement applications. Research institutions employ rubidium extensively in laser cooling and atom trapping experiments, where rubidium atoms are used to study quantum mechanical phenomena and develop new quantum technologies. The element serves as a crucial component in magnetometers used for geological surveys, mineral exploration, and magnetic field measurements in scientific research. Rubidium compounds are used in specialized glass manufacturing, where they can improve certain optical properties and chemical durability of glass products. The medical field has investigated rubidium compounds for potential applications in cardiac imaging and as radiotracers in positron emission tomography (PET) scans. Rubidium's high reactivity makes it useful in specialized chemical synthesis reactions and as a catalyst in certain organic chemistry applications. The aerospace industry has explored rubidium ion thrusters for spacecraft propulsion systems, where the element's properties could provide efficient propulsion for long-duration space missions. Research continues into rubidium's potential applications in quantum computing, where rubidium atoms show promise for quantum information storage and processing. The element also finds niche applications in specialized batteries and energy storage systems where its unique electrochemical properties offer advantages.
Rubidium's most widespread application is in the atomic clocks that synchronize GPS satellites, making accurate navigation possible for billions of users worldwide through smartphones, vehicles, and aircraft. Telecommunications companies rely on rubidium frequency standards to maintain precise timing across fiber optic networks and cellular systems. Scientific research facilities use rubidium vapor cells in laser systems for spectroscopy and precision measurements of fundamental physical constants. Geological survey teams employ rubidium magnetometers to map underground mineral deposits and study the Earth's magnetic field variations. Military and defense applications include rubidium-based navigation systems that provide GPS-independent positioning capabilities for critical operations. Medical imaging facilities use rubidium-82 generators for cardiac PET scans to diagnose heart disease and evaluate cardiac function. Research laboratories worldwide utilize rubidium in experiments studying Bose-Einstein condensates and other exotic states of matter. The oil and gas industry employs rubidium magnetometers in exploration activities to locate potential drilling sites and map subsurface geological structures. Specialty glass manufacturers incorporate rubidium compounds to produce high-performance optical components for telescopes and precision instruments. Academic institutions use rubidium atoms in physics demonstrations and experiments to teach quantum mechanics and atomic physics concepts. Even consumer applications benefit indirectly from rubidium through the precise timing systems that enable high-speed internet, digital television, and wireless communications. The renewable energy sector investigates rubidium-based energy storage systems for grid-scale applications where precise timing and control are essential.
Where it comes from
90 mg/kg of Earth's crust · more abundant than 82% of elements
Rubidium is a relatively rare alkali metal with an average concentration of approximately 90 parts per million in the Earth's crust, making it more abundant than lithium but less common than other alkali metals like sodium and potassium. The element never occurs as a free metal in nature due to its extreme reactivity with water and oxygen, instead being found as compounds in various minerals and geological formations. Rubidium commonly substitutes for potassium in potassium-bearing minerals due to their similar ionic radii and chemical properties, though in much smaller concentrations. Lepidolite, a lithium-bearing mica, contains the highest concentrations of rubidium found in nature, with some samples containing up to 3% rubidium oxide. Pollucite, a cesium aluminum silicate mineral, also contains significant amounts of rubidium as a substitute for cesium in the crystal structure. Carnallite, a potassium magnesium chloride mineral found in evaporite deposits, contains trace amounts of rubidium that accumulate during the mineral's formation. Seawater contains very low concentrations of rubidium, approximately 0.12 parts per million, making oceanic extraction economically unfeasible despite the vast volume of the oceans. Salt lake brines, particularly those with high potassium content, can contain elevated rubidium concentrations and represent a potential source for commercial extraction. Some clay minerals and feldspars contain rubidium as a trace element, though these sources are not economically viable for rubidium production. The element is also found in small quantities in some igneous rocks, particularly granite and pegmatite formations where it concentrates during the final stages of crystallization. Most commercial rubidium is obtained as a byproduct of lithium production from lepidolite or as a byproduct of cesium extraction from pollucite. The geographic distribution of rubidium resources is closely tied to lithium and cesium deposits, with significant sources in Canada, Zimbabwe, and parts of the United States.
Handling
Rubidium metal presents significant safety hazards due to its extreme reactivity with water and oxygen, requiring specialized handling procedures and storage conditions to prevent dangerous reactions. The pure metal must be stored under inert atmospheres or in mineral oil to prevent oxidation and contact with moisture, as exposure to air or water can cause violent reactions producing hydrogen gas and heat. Direct contact with rubidium metal should be avoided, as it can cause severe chemical burns to skin and eyes, and any contact requires immediate flushing with large amounts of water despite the potential for reaction. Rubidium compounds, while generally less hazardous than the metallic form, can still cause irritation to skin, eyes, and respiratory systems, requiring proper protective equipment during handling. Inhalation of rubidium dust or vapors should be prevented through adequate ventilation and respiratory protection, as exposure can cause respiratory irritation and potential systemic effects. The element's radioactive isotopes, particularly rubidium-87, require additional radiation safety precautions, though the natural isotope has an extremely long half-life and presents minimal radiation hazard under normal conditions. Laboratory workers handling rubidium must be trained in proper techniques for managing highly reactive metals and should have emergency procedures readily available. Fire suppression around rubidium requires special consideration, as water-based systems can exacerbate fires involving alkali metals, making dry powder or inert gas systems more appropriate. Storage areas for rubidium must be equipped with appropriate ventilation, fire suppression systems, and emergency response equipment suitable for reactive metal fires. Disposal of rubidium and its compounds requires specialized procedures and facilities capable of handling reactive materials safely. Pregnant women should avoid exposure to rubidium compounds, and all personnel should undergo appropriate safety training before working with this highly reactive element. Emergency response procedures should include protocols for treating chemical burns and managing fires involving alkali metals.
Quick answers
Rubidium (symbol Rb) is element 37 on the periodic table, a alkali metal in period 5, group 1. A soft alkali metal whose spectral line is deep red, and whose ions run some of the world's most precise clocks. At room temperature it is a solid.
[Kr] 5s¹, giving 5 occupied shells holding 2, 8, 18, 8, 1 electrons respectively.Rubidium melts at 312.5 K (39.3 °C) and boils at 961 K (687.9 °C).
The standard atomic weight of Rubidium is 85.468 u. That is a weighted average across its naturally occurring isotopes, which is why it is rarely a whole number.
Rubidium has a density of 1.532 g/cm³. Water is 1.0 g/cm³, so a block of rubidium is about 1.5× heavier.
Rubidium has a Pauling electronegativity of 0.82. The scale runs from 0.70 (francium, the least greedy for electrons) to 3.98 (fluorine, the most). A value this low means it readily gives its outer electrons away, forming positive ions.
Rubidium was discovered in 1861 by Bunsen & Kirchhoff. It is named after latin rubidus, "deep red" — its spectral line.
Rubidium makes up about 90 mg/kg of the Earth's crust — uncommon, but not rare.