Rubidium
Rubidium is a soft, silvery alkali metal so reactive that it must be stored away from air and water, much like its neighbors sodium and potassium. It's most famous today not for any industrial bulk use but for its precision role in some of the most accurate clocks ever built.
- Group · Period
- 1 · 5
- At room temp
- solid
- Melts at
- 312.46 K
- Density
- 1.53 g/cm³
- Discovered
- 1861
Uses
Rubidium’s most important practical application is in atomic clocks, which use the extremely regular frequency of rubidium atoms to keep time with remarkable precision. These clocks are compact and reliable enough to be used in telecommunications networks, navigation systems, and as backup timing references aboard GPS satellites, complementing the even more precise cesium clocks used as the primary standard. Rubidium compounds also color fireworks with a subtle red-violet hue.
In research, rubidium atoms are a favorite tool for physicists studying matter at extremely low temperatures, since they can be cooled and trapped with lasers relatively easily. This approach was used to create the first Bose-Einstein condensate in 1995, a state of matter where atoms behave collectively in ways normally seen only at the quantum scale, earning its creators a Nobel Prize.
History
Rubidium was discovered in 1861 by German scientists Robert Bunsen and Gustav Kirchhoff, who had recently developed spectroscopy as a way to identify elements by the unique pattern of light they emit when heated in a flame. While analyzing the mineral lepidolite, they noticed two previously unrecorded dark red lines in its spectrum, signaling a new element hiding within the sample. They named it rubidium, from the Latin word rubidus, meaning deepest red, directly after the spectral lines that had revealed its presence.
Fun facts
- Rubidium was discovered by studying the distinctive dark red lines it produced in a spectroscope, which is where its name comes from — 'rubidus' means deepest red in Latin.
- Rubidium atomic clocks are compact and reliable enough to serve as backup timing standards aboard GPS satellites.
- In 1995, physicists created the first Bose-Einstein condensate — a strange, ultra-cold state of matter — by cooling rubidium atoms to nearly absolute zero.
Frequently asked questions
How reactive is rubidium?
Extremely — like sodium and potassium above it in the periodic table, rubidium reacts violently with water, and it ignites spontaneously in air if left unprotected. It's normally stored under mineral oil or in a sealed, inert atmosphere to keep it away from moisture and oxygen.
How was rubidium actually discovered?
German chemists Robert Bunsen and Gustav Kirchhoff found it in 1861 using spectroscopy, a then-new technique they had pioneered that identifies elements by the specific colors of light they emit when heated. Rubidium revealed itself through two previously unseen deep red spectral lines in a mineral sample.
What is rubidium actually used for?
Its biggest practical role is in atomic clocks, where rubidium's extremely regular atomic vibrations provide a highly stable time reference used in telecommunications equipment and as a backup standard aboard GPS satellites. It's also a common tool in physics research involving ultra-cold atoms.
Compounds
4 notable compounds containing Rb
- Rb2CO3salt
Rubidium carbonate
A hygroscopic white salt used chiefly as a starting material for other rubidium compounds and in specialty high-index optical glass.
Used for: Additive in high-refractive-index optical glass and fiber optics
- RbClsalt
Rubidium chloride
A simple white ionic salt and the most common laboratory source of rubidium, used as a biological tracer because it behaves like potassium in living cells.
Used for: Cell-biology tracer for potassium transport; ceramic glazes
- RbOHbase
Rubidium hydroxide
A strongly corrosive, highly water-soluble alkali hydroxide, among the strongest bases known due to rubidium's large, weakly polarizing cation.
Used for: Electrolyte component in some specialty batteries
- RbNO3salt
Rubidium nitrate
A white crystalline oxidizer salt used mainly as a laboratory source of rubidium ion and in some specialty pyrotechnic formulations.
Used for: Pyrotechnics and specialty glass and ceramics
Isotopes
35 known isotopes
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| Isotope | Natural abundance | Half-life | Decay mode | Mass excess | Binding energy / nucleon | Decay width |
|---|---|---|---|---|---|---|
| Rb-85 stable | 72.17% | Stable | — | -82,167.34 keV | 8,697.44 keV | — |
| Rb-87 | 27.83% | 4.97E+10 Y | Beta-minus decay (100%) | -84,597.8 keV | 8,710.98 keV | 2.91 × 10-34 eV |
Show all 35 isotopes
| Rb-72 | — | 103 ns | Proton emission, Electron capture / beta-plus decay | -38,330 keV | 8,202 keV | 4.43 × 10-9 eV |
| Rb-73 | — | 81 ns | Proton emission, Electron capture / beta-plus decay | -46,011.61 keV | 8,305.08 keV | 5.63 × 10-9 eV |
| Rb-74 | — | 64.776 ms | Electron capture / beta-plus decay (100%) | -51,916.02 keV | 8,381.71 keV | 7.04 × 10-15 eV |
| Rb-75 | — | 19.0 s | Electron capture / beta-plus decay (100%) | -57,218.7 keV | 8,448.28 keV | 2.40 × 10-17 eV |
| Rb-76 | — | 36.5 s | Electron capture / beta-plus decay (100%), ECA (3.8e-7%) | -60,479.09 keV | 8,486.22 keV | 1.25 × 10-17 eV |
| Rb-77 | — | 3.78 m | Electron capture / beta-plus decay (100%) | -64,830.5 keV | 8,537.34 keV | 2.01 × 10-18 eV |
| Rb-78 | — | 17.66 m | Electron capture / beta-plus decay (100%) | -66,935.43 keV | 8,558.35 keV | 4.31 × 10-19 eV |
| Rb-79 | — | 22.9 m | Electron capture / beta-plus decay (100%) | -70,802.78 keV | 8,601.14 keV | 3.32 × 10-19 eV |
| Rb-80 | — | 33.4 s | Electron capture / beta-plus decay (100%) | -72,175.48 keV | 8,611.68 keV | 1.37 × 10-17 eV |
| Rb-81 | — | 4.572 h | Electron capture / beta-plus decay (100%) | -75,456.7 keV | 8,645.51 keV | 2.77 × 10-20 eV |
| Rb-82 | — | 1.2575 m | Electron capture / beta-plus decay (100%) | -76,187.81 keV | 8,647.43 keV | 6.05 × 10-18 eV |
| Rb-83 | — | 86.2 d | Electron capture (100%) | -79,070.64 keV | 8,675.22 keV | 6.13 × 10-23 eV |
| Rb-84 | — | 32.82 d | Electron capture / beta-plus decay (96.1%), Beta-minus decay (3.9%) | -79,758.98 keV | 8,676.22 keV | 1.61 × 10-22 eV |
| Rb-86 | — | 18.642 d | Beta-minus decay (99.9948%), Electron capture (0.0052%) | -82,747 keV | 8,696.9 keV | 2.83 × 10-22 eV |
| Rb-88 | — | 17.773 m | Beta-minus decay (100%) | -82,609 keV | 8,681.12 keV | 4.28 × 10-19 eV |
| Rb-89 | — | 15.32 m | Beta-minus decay (100%) | -81,712.4 keV | 8,664.19 keV | 4.96 × 10-19 eV |
| Rb-90 | — | 158 s | Beta-minus decay (100%) | -79,365.57 keV | 8,631.53 keV | 2.89 × 10-18 eV |
| Rb-91 | — | 58.2 s | Beta-minus decay (100%) | -77,745.05 keV | 8,607.56 keV | 7.84 × 10-18 eV |
| Rb-92 | — | 4.48 s | Beta-minus decay (100%), Beta-minus, neutron emission (0.0107%) | -74,772.45 keV | 8,569.42 keV | 1.02 × 10-16 eV |
| Rb-93 | — | 5.84 s | Beta-minus decay (100%), Beta-minus, neutron emission (1.39%) | -72,619.9 keV | 8,540.92 keV | 7.81 × 10-17 eV |
| Rb-94 | — | 2.702 s | Beta-minus decay (100%), Beta-minus, neutron emission (10.5%) | -68,562.79 keV | 8,492.76 keV | 1.69 × 10-16 eV |
| Rb-95 | — | 377.7 ms | Beta-minus decay (100%), Beta-minus, neutron emission (8.7%) | -65,890.31 keV | 8,460.2 keV | 1.21 × 10-15 eV |
| Rb-96 | — | 203 ms | Beta-minus decay (100%), Beta-minus, neutron emission (13.3%) | -61,354.35 keV | 8,408.9 keV | 2.25 × 10-15 eV |
| Rb-97 | — | 169.1 ms | Beta-minus decay (100%), Beta-minus, neutron emission (25.5%), B-2N | -58,519.15 keV | 8,376.19 keV | 2.70 × 10-15 eV |
| Rb-98 | — | 115 ms | Beta-minus decay (100%), Beta-minus, neutron emission (14.3%), B-2N (0.054%) | -54,369.15 keV | 8,330.73 keV | 3.97 × 10-15 eV |
| Rb-99 | — | 54 ms | Beta-minus decay (100%), Beta-minus, neutron emission (19.8%), B-2N | -51,121.15 keV | 8,295.3 keV | 8.45 × 10-15 eV |
| Rb-100 | — | 52 ms | Beta-minus decay (100%), Beta-minus, neutron emission (5.6%), B-2N (0.15%) | -46,265.88 keV | 8,244.51 keV | 8.77 × 10-15 eV |
| Rb-101 | — | 32 ms | Beta-minus decay (100%), Beta-minus, neutron emission (28%) | -42,567.42 keV | 8,206.18 keV | 1.43 × 10-14 eV |
| Rb-102 | — | 37 ms | Beta-minus decay (100%), Beta-minus, neutron emission (18%) | -37,252.31 keV | 8,152.74 keV | 1.23 × 10-14 eV |
| Rb-103 | — | 23 ms | Beta-minus decay (100%), Beta-minus, neutron emission, B-2N | -33,160 keV | 8,112 keV | 1.98 × 10-14 eV |
| Rb-104 | — | — | Beta-minus decay (100%), Beta-minus, neutron emission, B-2N | -27,450 keV | 8,057 keV | — |
| Rb-105 | — | — | Beta-minus decay (100%), Beta-minus, neutron emission, B-2N | — | — | — |
| Rb-106 | — | — | Beta-minus decay (100%), B-3N, B-2N | — | — | — |