Rb 37

Rubidium (Rb)

alkali-metal

Period: 5 Group: 1 Block: s

Solid

Standard Atomic Weight

Electron configuration

[Kr] 5s¹

Melting point

39.31 °C (312.46 K)

Boiling point

687.85 °C (961 K)

Density

1530 kg/m³

Oxidation states

−1, +1

Electronegativity (Pauling)

0.82

Ionization energy (1st)

Discovery year

1861

Atomic radius

235 pm

Details

Name origin Latin: rubidus (deep red); the color its salts impart to flames.

Discovery country Germany

Discoverers R. Bunsen, G. Kirchoff

Rubidium is a soft alkali metal of group 1, chemically close to potassium and cesium. Natural rubidium is a mixture dominated by stable ⁸⁵Rb with radioactive ⁸⁷Rb, whose very long half-life makes it important in geochronology. The element is not mined as a principal metal; it is obtained from minerals and brines where it substitutes for potassium. Its low ionization energy and convenient atomic transitions make rubidium useful in precision physics.

Rubidium can be liquid at room temperature. It is a soft, silvery-white metallic element of the alkali group and is the second most electropositive and alkaline element. It ignites spontaneously in air and reacts violently in water, setting fire to the liberated hydrogen. As with other alkali metals, it forms amalgams with mercury and it alloys with gold, cesium, sodium, and potassium. It colors a flame yellowish violet. Rubidium metal can be prepared by reducing rubidium chloride with calcium, and by a number of other methods. It must be kept under a dry mineral oil or in a vacuum or inert atmosphere.

The name derives from the Latin rubidus for "deepest red" because of the two deep red lines in its spectra. Rubidium was discovered in the mineral lepidolite by the German chemist Robert Wilhelm Bunsen and the German physicist Gustav-Robert Kirchoff in 1861. Bunsen isolated rubidium in 1863.

Rubidium was discovered by the German chemists Robert Bunsen and Gustav Kirchhoff in 1861 while analyzing samples of the mineral lepidolite (KLi2Al(Al, Si)3O10(F, OH)2) with a device called a spectroscope. The sample produced a set of deep red spectral lines they had never seen before. Bunsen was eventually able to isolate samples of rubidium metal. Today, most rubidium is obtained as a byproduct of refining lithium.

From the Latin word rubidus, deepest red. Discovered in 1861 by Bunsen and Kirchoff in the mineral lepidolite by use of the spectroscope.

Read about Rubidium on Wikipedia

Images

Properties

Physical

Atomic radius (empirical) 235 pm

Covalent radius 220 pm

Van der Waals radius 303 pm

Metallic radius 216 pm

Density

Molar volume 0.0559 L/mol

Phase at STP solid

Melting point 39.31 °C

Boiling point 687.85 °C

Thermal conductivity 58.2 W/(m·K)

Specific heat capacity 0.363 J/(g·K)

Molar heat capacity 31.06 J/(mol·K)

Crystal structure bcc

Chemical

Electronegativity (Pauling) 0.82

Electronegativity (Allen) 0.706

Electron affinity

Ionization energy (1st)

Ionization energy (2nd)

Ionization energy (3rd)

Ionization energy (4th)

Ionization energy (5th)

Oxidation states −1, +1

Valence electrons 1

Electron configuration

Electron configuration (semantic)

Thermodynamic

Triple point (temperature) 39.26 °C

Critical point (temperature) 1820 °C

Critical point (pressure) 1.600000e+7 Pa

Heat of fusion 0.02269783 eV

Heat of vaporization 0.71513707 eV

Heat of sublimation 0.84987304 eV

Heat of atomization 0.84987304 eV

Atomization enthalpy

Nuclear

Stable isotopes 1

Discovery year 1861

Abundance

Abundance (Earth's crust) 90 mg/kg

Abundance (ocean)

Reactivity

N/A

Crystal Structure

Lattice constant a 559 pm

Electronic Structure

Electrons per shell 2, 8, 18, 8, 1

Identifiers

CAS number 7440-17-7

Term symbol

InChI InChI=1S/Rb

InChI Key IGLNJRXAVVLDKE-UHFFFAOYSA-N

Electron Configuration Measured

Ion charge

Protons 37

Electrons 37

Charge Neutral

Configuration Rb: 5s¹

[Kr] 5s¹

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s¹

Orbital diagram

↑↓

2/2

↑↓

2/2

↑↓

6/6

↑↓

2/2

↑↓

6/6

↑↓

2/2

↑↓

10/10

↑↓

6/6

↑

1/2 1↑

Total electrons: 37 Unpaired: 1

Atomic model

Protons 37

Neutrons 48

Electrons 37

Mass number 85

Stability Stable

Isotopes change neutron count, mass, and stability — not the electron configuration of a neutral atom.

Schematic atomic model, not to scale.

Atomic Fingerprint

Emission / Absorption Spectrum

Emission Visible: 380–750 nm

Isotope Distribution

Mass number	Atomic mass (u)	Natural abundance	Half-life
85 Stable	84.9117897379 ± 0.0000000054	72.1700%	Stable

Measured

Phase / State

Solid 25 °C (298.15 K)

Reason: 14.3 °C below melting point (39.31 °C)

Melting point 39.31 °C

Boiling point 687.85 °C

Below melting by 14.3 °C

0 K Current temperature: 25 °C 6000 K

Phase timeline

Schematic, not to scale

Solid

Liquid

Gas

Melting

Boiling

25°C

Solid

Liquid

Gas

Current

Phase transition points

Melting point Literature

39.31 °C

Boiling point Literature

687.85 °C

Current phase Calculated
Solid

Transition energies

Heat of fusion Literature

0.02269783 eV

Energy required to melt 1 mol at melting point

Heat of vaporization Literature

0.71513707 eV

Energy required to vaporize 1 mol at boiling point

Heat of sublimation Literature

0.84987304 eV

Energy required to sublime 1 mol at sublimation point

Density

Reference density Literature

1530 kg/m³

At standard conditions

Current density Calculated

1530 kg/m³

At standard conditions

Advanced

Triple point Literature

39.26 °C

Critical point Literature

1820 °C

Atomic Spectra

Showing 10 of 37 Atomic Spectra. Sorted by ion charge (ascending).

Lines Holdings ?

Ion	Charge	Total lines	Transition probabilities	Level designations
Rb I	0	213	40	213
Rb II	+1	699	49	602
Rb III	+2	232	0	230
Rb IV	+3	573	0	573
Rb V	+4	34	13	34
Rb VI	+5	34	32	34
Rb VII	+6	26	10	26
Rb VIII	+7	34	26	34
Rb IX	+8	40	17	40
Rb X	+9	64	29	64

NIST Lines Holdings →

Levels Holdings ?

Ion	Charge	Levels
Rb I	0	240
Rb II	+1	166
Rb III	+2	92
Rb IV	+3	131
Rb V	+4	21
Rb VI	+5	20
Rb VII	+6	21
Rb VIII	+7	25
Rb IX	+8	37
Rb X	+9	41

NIST Levels Holdings →

37 Rb 85.4678

Rubidium — Atomic Orbital Visualizer

[Kr]5s1

Energy levels 2 8 18 8 1

Oxidation states -1, +1

HOMO 5s n=5 · l=0 · m=0

Rubidium — Atomic Orbital Visualizer Preview

Three.js loads only on request

37 Rb 85.4678

Rubidium — Crystal Structure Visualizer

Body-Centered Cubic · Pearson cI2

Experimental

Pearson cI2

Coord. № 8

Packing 68.000%

Rubidium — Crystal Structure Visualizer Preview

Three.js loads only on request

Ionic Radii

Charge	Coordination	Spin	Radius
+1	6	N/A	152 pm
+1	7	N/A	156 pm
+1	8	N/A	161 pm
+1	9	N/A	163 pm
+1	10	N/A	166 pm
+1	11	N/A	169 pm
+1	12	N/A	172 pm
+1	14	N/A	183 pm

Compounds

85.468 u

Rb+

85.468 u

81.918 u

Rb+

81.918 u

85.911 u

86.909 u

83.914 u

80.919 u

84.912 u

88.912 u

87.911 u

82.915 u

78.924 u

Rb+

84.912 u

79.923 u

Rb+

85.911 u

Rb+

80.919 u

Isotopes (1)

Twenty four isotopes of rubidium are known. Naturally occurring rubidium is made of two isotopes, 85Rb and 87Rb. Rubidium-87 is present to the extent of 27.85% in natural rubidium and is a beta emitter with a half-life of 4.9 x 1010 years. Ordinary rubidium is sufficiently radioactive to expose a photographic film in about 30 to 60 days. Rubidium forms four oxides: Rb2O, Rb2O2, Rb2O3, Rb2O4.

	Mass number	Atomic mass (u)	Natural abundance	Half-life	Decay mode
	85 Stable	84.9117897379 ± 0.0000000054	72.1700% ± 0.0200%	Stable	stable

85 Stable

Atomic mass (u) 84.9117897379 ± 0.0000000054

Natural abundance 72.1700% ± 0.0200%

Half-life Stable

Decay mode

stable

Spectral Lines

Showing 50 of 202 Spectral Lines. Only spectral lines with measured intensity are shown by default.

Wavelength (nm)	Intensity	Ion stage	Type	Transition	Accuracy	Source
424.439 nm	90000	Rb II	emission	4p5.(2P<3/2>).5s 2[3/2] → 4p5.(2P*<3/2>).5p 2[5/2]	Measured	NIST
477.5954 nm	30000	Rb II	emission	4p5.(2P<3/2>).5s 2[3/2] → 4p5.(2P*<3/2>).5p 2[1/2]	Measured	NIST
394.051 nm	25000	Rb II	emission	4p5.(2P<3/2>).5s 2[3/2] → 4p5.(2P*<3/2>).5p 2[3/2]	Measured	NIST
457.1765 nm	20000	Rb II	emission	4p5.(2P<3/2>).5s 2[3/2] → 4p5.(2P*<3/2>).5p 2[5/2]	Measured	NIST
427.3141 nm	15000	Rb II	emission	4p5.(2P<3/2>).5s 2[3/2] → 4p5.(2P*<3/2>).5p 2[5/2]	Measured	NIST
464.8557 nm	10000	Rb II	emission	4p5.4d 3P* → 4p5.(2P*<1/2>).5p 2[3/2]	Measured	NIST
515.2081 nm	10000	Rb II	emission	4p5.(2P<3/2>).5s 2[3/2] → 4p5.(2P*<3/2>).5p 2[1/2]	Measured	NIST
645.833 nm	10000	Rb II	emission	4p5.(2P<1/2>).5s 2[1/2] → 4p5.(2P*<3/2>).5p 2[1/2]	Measured	NIST
552.2776 nm	5000	Rb II	emission	4p5.(2P<1/2>).5s 2[1/2] → 4p5.(2P*<3/2>).5p 2[3/2]	Measured	NIST
656.0799 nm	5000	Rb II	emission	4p5.4d 3F* → 4p5.(2P*<1/2>).5p 2[3/2]	Measured	NIST
419.3079 nm	3500	Rb II	emission	4p5.(2P<3/2>).5s 2[3/2] → 4p5.(2P*<3/2>).5p 2[3/2]	Measured	NIST
453.0333 nm	3000	Rb II	emission	4p5.4d 3P* → 4p5.(2P*<1/2>).5p 2[1/2]	Measured	NIST
380.1896 nm	2500	Rb II	emission	4p5.(2P<1/2>).5s 2[1/2] → 4p5.(2P*<1/2>).5p 2[1/2]	Measured	NIST
437.7123 nm	2500	Rb II	emission	4p5.(2P<3/2>).5p 2[5/2] → 4p5.(2P<3/2>).6s 2[3/2]*	Measured	NIST
402.9485 nm	1700	Rb II	emission	4p5.(2P<3/2>).5s 2[3/2] → 4p5.(2P*<3/2>).5p 2[3/2]	Measured	NIST
429.3971 nm	1500	Rb II	emission	4p5.(2P<3/2>).5s 2[3/2] → 4p5.(2P*<3/2>).5p 2[3/2]	Measured	NIST
382.66591 nm	1000	Rb II	emission	4p5.(2P<3/2>).5p 2[3/2] → 4p5.(2P<3/2>).5d 2[3/2]*	Measured	NIST
420.18053 nm	1000	Rb I	emission	4p6.5s 2S → 4p6.6p 2P*	Measured	NIST
434.6961 nm	1000	Rb II	emission	4p5.(2P<3/2>).5p 2[5/2] → 4p5.(2P<3/2>).6s 2[3/2]*	Measured	NIST
446.9475 nm	1000	Rb II	emission	4p5.(2P<1/2>).5p 2[3/2] → 4p5.(2P<1/2>).6s 2[1/2]*	Measured	NIST
473.0454 nm	1000	Rb II	emission	4p5.4d 3P* → 4p5.(2P*<1/2>).5p 2[1/2]	Measured	NIST
475.5304 nm	1000	Rb II	emission	4p5.(2P<3/2>).5p 2[3/2] → 4p5.(2P<3/2>).6s 2[3/2]*	Measured	NIST
655.5619 nm	1000	Rb II	emission	4p5.4d 3P* → 4p5.(2P*<3/2>).5p 2[3/2]	Measured	NIST
451.90262 nm	700	Rb II	emission	4p5.4d 1P* → 4p5.(2P*<3/2>).4f 2[3/2]	Measured	NIST
392.22011 nm	500	Rb II	emission	4p5.(2P<3/2>).5p 2[3/2] → 4p5.(2P<3/2>).5d 2[1/2]*	Measured	NIST
421.5539 nm	500	Rb I	emission	4p6.5s 2S → 4p6.6p 2P*	Measured	NIST
426.6584 nm	500	Rb II	emission	4p5.(2P<3/2>).5p 2[5/2] → 4p5.(2P<3/2>).6s 2[3/2]*	Measured	NIST
465.9284 nm	500	Rb II	emission	4p5.(2P<3/2>).5p 2[3/2] → 4p5.(2P<3/2>).6s 2[3/2]*	Measured	NIST
551.2542 nm	500	Rb II	emission	4p5.4d 3F* → 4p5.(2P*<1/2>).5p 2[3/2]	Measured	NIST
386.07454 nm	450	Rb II	emission	4p5.(2P<3/2>).5p 2[1/2] → 4p5.(2P<3/2>).6s 2[3/2]*	Measured	NIST
454.0732 nm	400	Rb II	emission	4p5.(2P<3/2>).5p 2[3/2] → 4p5.(2P<3/2>).6s 2[3/2]*	Measured	NIST
444.00924 nm	300	Rb II	emission	4p5.4d 1P* → 4p5.(2P*<3/2>).4f 2[5/2]	Measured	NIST
516.4575 nm	300	Rb II	emission	4p5.(2P<1/2>).5s 2[1/2] → 4p5.(2P*<3/2>).5p 2[3/2]	Measured	NIST
626.94 nm	300	Rb II	emission	4p5.(2P<3/2>).4f 2[9/2] → 4p5.(2P<3/2>).6g 2[11/2]*	Measured	NIST
390.7292 nm	250	Rb II	emission	4p5.(2P<3/2>).5p 2[3/2] → 4p5.(2P<3/2>).5d 2[1/2]*	Measured	NIST
542.244 nm	250	Rb II	emission	4p5.4d 1P* → 4p5.(2P*<3/2>).6p 2[3/2]	Measured	NIST
527.0514 nm	200	Rb II	emission	4p5.(2P<3/2>).5p 2[1/2] → 4p5.(2P<3/2>).6s 2[3/2]*	Measured	NIST
573.9645 nm	200	Rb II	emission	4p5.(2P<3/2>).5d 2[7/2] → 4p5.(2P*<3/2>).5f 2[9/2]	Measured	NIST
613.5268 nm	200	Rb II	emission	4p5.(2P<3/2>).5d 2[5/2] → 4p5.(2P*<3/2>).5f 2[7/2]	Measured	NIST
383.78512 nm	175	Rb II	emission	4p5.(2P<3/2>).5p 2[3/2] → 4p5.(2P<3/2>).5d 2[1/2]*	Measured	NIST
740.8171 nm	150	Rb I	emission	4p6.5p 2P* → 4p6.7s 2S	Measured	NIST
550.0635 nm	100	Rb II	emission	4p5.(2P<3/2>).6p 2[5/2] → 4p5.(2P<3/2>).7d 2[7/2]*	Measured	NIST
627.5697 nm	100	Rb II	emission	4p5.(2P<3/2>).4f 2[9/2] → 4p5.(2P<3/2>).6g 2[11/2]*	Measured	NIST
451.9884 nm	75	Rb II	emission	4p5.(2P<3/2>).5d 2[5/2] → 4p5.(2P*<3/2>).6f 2[7/2]	Measured	NIST
459.989 nm	75	Rb II	emission	4p5.(2P<3/2>).5d 2[5/2] → 4p5.(2P*<3/2>).6f 2[7/2]	Measured	NIST
543.1528 nm	75	Rb I	emission	4p6.5p 2P* → 4p6.8d 2D	Measured	NIST
589.308 nm	75	Rb II	emission	4p5.(2P<3/2>).5d 2[7/2] → 4p5.(2P*<3/2>).5f 2[9/2]	Measured	NIST
607.0751 nm	75	Rb I	emission	4p6.5p 2P* → 4p6.8s 2S	Measured	NIST
614.0319 nm	75	Rb II	emission	4p5.4d 3F* → 4p5.(2P*<1/2>).5p 2[3/2]	Measured	NIST
572.4125 nm	60	Rb I	emission	4p6.5p 2P* → 4p6.7d 2D	Measured	NIST

Extended Properties

Covalent Radii (Extended)

Covalent radius (Pyykkö)

Covalent radius (Pyykkö, double)

Covalent radius (Bragg)

Van der Waals Radii

Truhlar

Batsanov

Alvarez

UFF

MM3

Atomic & Metallic Radii

Atomic radius (Rahm)

Metallic radius (C12)

Numbering Scales

Mendeleev

Pettifor

Glawe

Electronegativity Scales

Ghosh

Miedema

Gunnarsson–Lundqvist

Robles–Bartolotti

Polarizability & Dispersion

Dipole polarizability

Dipole polarizability (unc.)

C₆

C₆ (Gould–Bučko)

Miedema Parameters

Miedema molar volume

Miedema electron density

Phase Transitions & Allotropes

Melting point	312.45 K
Boiling point	961.15 K
Critical point (temperature)	2093.15 K
Critical point (pressure)	16 MPa
Triple point (temperature)	312.41 K

Oxidation State Categories

+1 main

−1 extended

Advanced Reference Data

Screening Constants (9)

n	Orbital	σ
1	s	0.7922
2	p	3.9612
2	s	9.8432
3	d	15.3208
3	p	15.6967
3	s	15.1573
4	p	26.1192
4	s	24.612
5	s	32.0155

Crystal Radii Detail (8)

Charge	CN	r_crystal (pm)	Origin
1	VI	166
1	VII	170
1	VIII	175
1	IX	177	estimated,
1	X	180
1	XI	183
1	XII	186
1	XIV	197

Isotope Decay Modes (61)

Isotope	Mode	Intensity
71	p	—
72	p	—
73	B+	—
73	p	100%
74	B+	100%
74	B+p	—
75	B+	100%
76	B+	100%
76	B+A	3.8%
77	B+	100%

X‑ray Scattering Factors (508)

Energy (eV)	f₁	f₂
10	—	0.06968
10.1617	—	0.07104
10.3261	—	0.07253
10.4931	—	0.07441
10.6628	—	0.07635
10.8353	—	0.07833
11.0106	—	0.08037
11.1886	—	0.083
11.3696	—	0.08599
11.5535	—	0.0891

Additional Data

Estimated Crustal Abundance

The estimated element abundance in the earth's crust.

9.0×101 milligrams per kilogram

References (1)

[5] Rubidium https://education.jlab.org/itselemental/ele037.html

Estimated Oceanic Abundance

The estimated element abundance in the earth's oceans.

1.2×10-1 milligrams per liter

References (1)

[5] Rubidium https://education.jlab.org/itselemental/ele037.html

Sources

Sources of this element.

The element is much more abundant than was thought several years ago. It is now considered to be the 16th most abundant element in the earth's crust. Rubidium occurs in pollucite, leucite, and zinnwaldite, which contains traces up to 1%, in the form of the oxide. It is found in lepidolite to the extent of about 1.5%, and is recovered commercially from this source. Potassium minerals, such as those found at Searles Lake, California, and potassium chloride recovered from the brines in Michigan also contain the element and are commercial sources. It is also found along with cesium in the extensive deposits of pollucite at Bernic Lake, Manitoba.

References (1)

[6] Rubidium https://periodic.lanl.gov/37.shtml

References

(9)

1 PubChem

Data deposited in or computed by PubChem

Visit source

2 Atomic Mass Data Center (AMDC), International Atomic Energy Agency (IAEA)

The half-life and atomic mass data was provided by the Atomic Mass Data Center at the International Atomic Energy Agency.

Visit source License

3 IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW)

Rubidium

Element data are cited from the Atomic weights of the elements (an IUPAC Technical Report). The IUPAC periodic table of elements can be found at https://iupac.org/what-we-do/periodic-table-of-elements/. Additional information can be found within IUPAC publication doi:10.1515/pac-2015-0703 Copyright © 2020 International Union of Pure and Applied Chemistry.

Visit source License

4 IUPAC Periodic Table of the Elements and Isotopes (IPTEI)

The information are cited from Pure Appl. Chem. 2018; 90(12): 1833-2092, https://doi.org/10.1515/pac-2015-0703.

Visit source License

License note: Copyright (c) 2020 International Union of Pure and Applied Chemistry. The International Union of Pure and Applied Chemistry (IUPAC) contribution within Pubchem is provided under a CC-BY-NC-ND 4.0 license, unless otherwise stated.

5 Jefferson Lab, U.S. Department of Energy

Rubidium

Thomas Jefferson National Accelerator Facility (Jefferson Lab) is one of 17 national laboratories funded by the U.S. Department of Energy. The lab's primary mission is to conduct basic research of the atom's nucleus using the lab's unique particle accelerator, known as the Continuous Electron Beam Accelerator Facility (CEBAF). For more information visit https://www.jlab.org/

Visit source License

License note: Please see citation and linking information: https://education.jlab.org/faq/index.html

6 Los Alamos National Laboratory, U.S. Department of Energy

Rubidium

The periodic table at the LANL (Los Alamos National Laboratory) contains basic element information together with the history, source, properties, use, handling and more. The provenance data may be found from the link under the source name.

Visit source License

7 NIST Physical Measurement Laboratory

Rubidium

The periodic table contains NIST's critically-evaluated data on atomic properties of the elements. The provenance data that include data for atomic spectroscopy, X-ray and gamma ray, radiation dosimetry, nuclear physics, and condensed matter physics may be found from the link under the source name. Ref: https://www.nist.gov/pml/atomic-spectra-database

Visit source License

8 PubChem Elements

Rubidium

This section provides all form of data related to element Rubidium.

License

9 PubChem Elements

Rubidium

The element property data was retrieved from publications.

License

Last updated: May 1, 2026