Rubidium (Rb)
Alkali metal
Rubidium is a soft alkali metal so reactive it ignites spontaneously in air and explodes on contact with water. Its ultra-regular atomic vibrations make it the timekeeper inside many atomic clocks and GPS satellites.
Position on the periodic table
Atomic properties
| Atomic number | 37 |
|---|---|
| Atomic mass | 85.4678 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 |
| Noble gas shorthand | [Kr] 5s1 |
| Electrons per shell | 2, 8, 18, 8, 1 |
| Valence electrons (outer shell) | 1 |
| Common oxidation states | +1 |
| Electronegativity (Pauling) | 0.82 |
| Covalent radius (approx.) | 220 pm |
| First ionization energy | 403 kJ/mol |
| Electron affinity | 46.9 kJ/mol |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Density | 1.532 g/cm³ |
| Melting point | 39.3 °C (312.45 K) |
| Boiling point | 687.85 °C (961 K) |
| Appearance | grey white |
| Radioactive | No |
| Origin | Occurs naturally |
Electron configuration of rubidium
Rubidium's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1, usually shortened to [Kr] 5s1. Its electrons occupy 5 shells (2, 8, 18, 8, 1), placing it in period 5 of the s-block. The 1 outer-shell electron drives its bonding behaviour. Explore it interactively in the electron configuration calculator.
Uses of rubidium
- Atomic clocks and GPS timing
- Specialty glasses and photocells
- Cold-atom physics research
Biological role: No essential role; rubidium ions behave a little like potassium in the body.
Occurrence: Widespread in trace amounts within potassium minerals like lepidolite.
Common compounds of rubidium
RbCl
Rubidium chloride
Rb2CO3
Rubidium carbonate
History and discovery
Discovered: 1861 — Robert Bunsen. Name origin: From Latin rubidus, deep red — the colour of its spectral lines.
Discovered spectroscopically in 1861 by Robert Bunsen and Gustav Kirchhoff via its red spectral lines.
Safety notes
Violently water-reactive; stored sealed under dry inert gas or oil.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Rubidium
1. What is the chemical symbol of Rubidium?
2. What is the atomic number of Rubidium?
3. Which category does Rubidium belong to?
4. What is the state of Rubidium at room temperature?
5. Which period of the periodic table is Rubidium in?
Rubidium FAQs
What is the atomic number of rubidium?
Rubidium's atomic number is 37 — every rubidium atom has 37 protons in its nucleus.
What is the symbol for rubidium?
Rb. From Latin rubidus, deep red — the colour of its spectral lines.
Is rubidium a metal, nonmetal, or metalloid?
Rubidium is classified as a alkali metal.
What state is rubidium at room temperature?
At about 25 °C, rubidium is a solid. It melts at 39.3 °C.
How many valence electrons does rubidium have?
Rubidium has 1 electron in its outer shell (shell pattern: 2, 8, 18, 8, 1).
What is rubidium used for?
Key uses include: atomic clocks and gps timing; specialty glasses and photocells; cold-atom physics research.
Related elements
Keep working with this element
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