Rubidium is a soft, highly reactive metal found alongside other alkali elements in minerals and brines. It has specialized research uses and has been used in photocells and particular glasses. Its chemical similarity to potassium makes comparison within a periodic-table column especially informative.
FROM ELEMENT TO APPLICATION
AN ELEMENT IN CONTEXT
How does a rubidium atomic response correct an electronic oscillator?
Rubidium-87 atoms in a vapor cell
FOLLOW THIS RELATIONSHIP
Prepare the atomic population
Light prepares rubidium-87 atoms in a selected energy-state distribution, allowing the instrument to probe an atomic response using a controlled optical and microwave system.
Explore the model (optional)
RbFORM → INTERACTION → CONSEQUENCE
Follow the explanation in either direction. These are authored steps, not a physical clock.
Atomic identity, reference properties and structure models
INTERACTIVE 3D37 visible sites
An electron censusDrag to rotate · scroll or pinch to zoom
[Kr] 5s1. Grouping electrons by principal shell connects the neutral-atom configuration to periodic-table patterns.
What this representation means
A three-dimensional counting diagram. Dots are count markers, not measured electron positions; spherical placement and spacing are arbitrary. There are no electron trajectories here. Orbitals describe quantum states.
Bunsen and Kirchhoff investigated the lepidolite in 1861 and detected previously unfamiliar red lines in its . Separation from potassium-bearing material helped establish rubidium as a distinct element. Its name commemorates the spectral color rather than the silvery appearance of the metal. The discovery shows how spectroscopy can reveal a small constituent whose broad chemical resemblance to another element would otherwise make identification difficult.
1861
Spectral identity recognized
Characteristic red spectral lines identified rubidium.
1928
Pure metal prepared
A pure sample became available after earlier discovery and separation work.
Rubidium occurs in minerals including lepidolite and pollucite and commonly accompanies potassium or cesium. Its association with chemically related elements explains why mineral separation and identification can be challenging. Natural rubidium contains more than one , adding a nuclear distinction within material that shares the same elemental identity.
Rubidium is a soft alkali metal that reacts strongly with air and water. It can also form with several other metals. Those metallic reactions differ from its role as individual atoms in a vapor cell, where carefully measured transitions between atomic energy states can provide a frequency reference.
Each section links its supporting references. Descriptions and diagrams were authored for this atlas. Source checks completed. Source checks dated 2026-09-06.
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Family labels and the group-3 layout are teaching conventions. A table position does not establish an unknown bulk property. Electronic configurations refer to neutral atoms; ions and material environments require their own account.
Read each reference property together with its units, conditions and the reference information below.
Not yet recorded: electron affinity, second ionization energy, ground-state term symbol, van der waals radius, thermal conductivity, specific heat capacity, electrical resistivity, crystal structure, lattice parameter a, space group, abundance in seawater, abundance in the universe, annual production, supply-risk listing, hazard classification, biological role, cas registry number, pubchem cid, wikidata item. These families are declared and awaiting an ingestion run against the source each names; they are listed here rather than shown as empty rows.
Physical
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Phase at 20 °C
solid
293.15 K, 101.325 kPa
Melting point in K
312.46 K
at standard pressure unless noted
Boiling point in K
961 K
101.325 kPa
Density in g/cm³
1.53 g/cm³
solids and liquids at 293 K; gases at 273 K and 101.325 kPa
Atomic and electronic
Intended reference: Pauling electronegativity scale · Widely tabulated; original in The Nature of the Chemical Bond
Electronegativity in Pauling
0.82 Pauling
Pauling scale
First ionization energy in kJ/mol
403 kJ/mol
gas-phase neutral atom, ground state
Covalent radius in pm
220 pm
single-bond covalent radius
Common oxidation states
+1
states met in ordinary compounds; not exhaustive
Occurrence and identity
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Abundance in the crust in mg/kg
90 mg/kg
upper continental crust, mass fraction
Has stable isotopes
Yesderived
Discovery year in CE
1861 CEderived
WHERE IT SITS AMONG ITS NEIGHBORS
Electronegativity across period 5
Rb 0.82 Pauling · Rubidium
Electronegativity across period 5. Exact values.
Rb
0.82
Sr
0.95
Y
1.22
Zr
1.33
Nb
1.6
Mo
2.16
Tc
1.9
Ru
2.2
Rh
2.28
Pd
2.2
Ag
1.93
Cd
1.69
In
1.78
Sn
1.96
Sb
2.05
Te
2.1
I
2.66
Xe
2.6
Electronegativity down group 1
Rb 0.82 Pauling · Rubidium
Electronegativity down group 1. Exact values.
H
2.2
Li
0.98
Na
0.93
K
0.82
Rb
0.82
Cs
0.79
The trend uses the same reference-property values as the periodic table. Elements with no recorded value are left out of the line rather than drawn at zero.
