Quick Facts
| Property | Value |
|---|---|
| Symbol | Rb |
| Atomic Number | 37 |
| Atomic Mass | 85.468 u |
| Category | Alkali Metal |
| Period | 5 |
| Group | 1 |
| Block | s |
| Electron Configuration | [Kr] 5s¹ |
Physical Properties
| Property | Value |
|---|---|
| State at 20°C | Solid |
| Density | 1.532 g/cm³ |
| Melting Point | 39.31°C (312.46 K) |
| Boiling Point | 688°C (961 K) |
| Appearance | Soft, silvery-white metal |
Atomic Properties
| Property | Value |
|---|---|
| Electron Configuration | [Kr] 5s¹ |
| Electronegativity | 0.82 (Pauling scale) |
| First Ionization Energy | 403.0 kJ/mol |
| Atomic Radius | 248 pm |
| Covalent Radius | 220 pm |
| Van der Waals Radius | 303 pm |
History and Discovery
Discovered by: Robert Bunsen and Gustav Kirchhoff Year of Discovery: 1861 Location: Heidelberg, Germany
Etymology
Named from the Latin "rubidus" meaning "deep red," after the prominent red lines in its emission spectrum.
Discovery Story
Robert Bunsen and Gustav Kirchhoff discovered rubidium in 1861 using their newly invented spectroscope. They analyzed the mineral lepidolite and observed previously unknown red spectral lines. This was one of the first elements discovered by spectroscopy.
Isotopes
| Isotope | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|
| ⁸⁵Rb | 72.17% | Stable | - |
| ⁸⁷Rb | 27.83% | 4.9 × 10¹⁰ years | β⁻ |
Occurrence
Natural Abundance
Rubidium is moderately rare, comprising about 90 ppm of Earth's crust. It is never found free due to its reactivity. It occurs in lepidolite, pollucite, and other minerals. No concentrated rubidium ores exist.
Extraction and Production
- Byproduct: From lithium and cesium extraction
- Lepidolite Processing: Main source
- Electrolysis: Of molten rubidium chloride
- Global production: 2-4 tons annually
Applications and Uses
Scientific Applications
- Atomic clocks (rubidium frequency standards)
- Bose-Einstein condensate research
- Magnetometers
- Laser cooling experiments
Electronics
- Photocells and photomultipliers
- Vacuum tubes (getter material)
- Ion propulsion research
Medical Applications
- Rubidium-82 for cardiac PET imaging
- Cancer detection (experimental)
Other Uses
- Specialty glasses
- Fireworks (purple color)
Biological Role
Rubidium has no known essential biological role but can substitute for potassium in some biological systems.
In the Human Body
- About 360 mg in adult body
- Follows potassium in metabolism
- No established biological function
Research
Some studies suggest rubidium may affect mood, leading to research on psychiatric applications.
Safety and Hazards
Toxicity
Rubidium has moderate toxicity. It can interfere with potassium-dependent processes.
Handling Precautions
- Highly reactive—ignites in air
- Reacts explosively with water
- Store under inert gas or mineral oil
- Causes severe burns
- More reactive than potassium
Environmental Impact
Rubidium is naturally occurring and generally not a significant environmental concern.
Interesting Facts
- Rubidium can be liquid on a warm day (melts at 39.31°C)
- Rubidium-87 is used to date geological formations
- Rubidium atomic clocks are used in GPS satellites
- It is one of the most electropositive elements
- Rubidium was the second element discovered by spectroscopy (after cesium)