Ra 88

Radium (Ra)

alkaline-earth-metal

Period: 7 Group: 2 Block: s

Solid

Standard Atomic Weight

Electron configuration

[Rn] 7s²

Melting point

699.85 °C (973 K)

Boiling point

1139.85 °C (1413 K)

Density

5000 kg/m³

Oxidation states

Electronegativity (Pauling)

0.9

Ionization energy (1st)

Discovery year

1898

Atomic radius

215 pm

Details

Name origin Latin: radius (ray).

Discovery country France

Discoverers Pierre and Marie Curie

Radium is a heavy alkaline earth metal and the element below barium in group 2. All of its isotopes are radioactive; ²²⁶Ra, with a half-life of about 1600 years, is the best known and occurs in uranium ores as part of the ²³⁸U decay series. Its chemistry is dominated by the Ra²⁺ ion, which resembles Ba²⁺ but is less commonly handled because intense radioactivity limits direct study.

Radium is obtained commercially as bromide and chloride; it is doubtful if any appreciable stock of the isolated element now exists. The pure metal is brilliant white when freshly prepared, but blackens on exposure to air, probably due to formation of the nitride. It exhibits luminescence, as do its slats; it decomposes in water and is somewhat more volatile than barium. It is a member of the alkaline-earth group of metals. Radium imparts a carmine red color to a flame. Radium emits alpha, beta, and gamma rays and when mixed with beryllium produce neutrons. One gram of 226Ra undergoes 3.7 x 1010 disintegrations per second. The curie is defined as that amount of radioactivity which has the same disintegration rate as 1 g of 226Ra. Twenty five isotopes are now known; radium 226, the common isotope, has a half-life of 1600 years.

Radium was discovered by Marie Sklodowska Curie, a Polish chemist, and Pierre Curie, a French chemist, in 1898. Marie Curie obtained radium from pitchblende, a material that contains uranium, after noticing that unrefined pitchblende was more radioactive than the uranium that was separated from it. She reasoned that pitchblende must contain at least one other radioactive element. Curie needed to refine several tons of pitchblende in order to obtain tiny amounts of radium and polonium, another radioactive element discovered by Curie. One ton of uranium ore contains only about 0.14 grams of radium. Today, radium can be obtained as a byproduct of refining uranium and is usually sold as radium chloride (RaCl2) or radium bromide (RaBr2) and not as a pure material. Radium's most stable isotope, radium-226, has a half-life of about 1600 years. It decays into radon-222 through alpha decay or into lead-212 by ejecting a carbon-14 nucleus.

Radium was discovered in 1898 by Madame Curie in the pitchblende or uraninite of North Bohemia, where it occurs. There is about 1 g of radium in 7 tons of pitchblende. The element was isolated in 1911 by Mme. Curie and Debierne by the electrolysis of a solution of pure radium chloride employing a mercury cathode; on distillation in an atmosphere of hydrogen, this amalgam yielded the pure metal.

Read about Radium on Wikipedia

Images

Properties

Physical

Atomic radius (empirical) 215 pm

Covalent radius 221 pm

Van der Waals radius 283 pm

Density

Molar volume 0.045 L/mol

Phase at STP solid

Melting point 699.85 °C

Boiling point 1139.85 °C

Chemical

Electronegativity (Pauling) 0.9

Electronegativity (Allen) 0.89

Electron affinity

Ionization energy (1st)

Ionization energy (2nd)

Ionization energy (3rd)

Ionization energy (4th)

Ionization energy (5th)

Oxidation states +2

Valence electrons 2

Electron configuration

Electron configuration (semantic)

Thermodynamic

Heat of fusion 0.08291444 eV

Heat of vaporization 1.171167 eV

Heat of sublimation 1.647925 eV

Heat of atomization 1.647925 eV

Atomization enthalpy

Nuclear

Stable isotopes 0

Mass number (most stable) 226

Discovery year 1898

Abundance

Abundance (Earth's crust) 9.000e-7 mg/kg

Abundance (ocean)

Reactivity

N/A

Crystal Structure

N/A

Electronic Structure

Electrons per shell 2, 8, 18, 32, 18, 8, 2

Identifiers

CAS number 7440-14-4

Term symbol

InChI InChI=1S/Ra

InChI Key HCWPIIXVSYCSAN-UHFFFAOYSA-N

Electron Configuration Measured

Ion charge

Protons 88

Electrons 88

Charge Neutral

Configuration Ra: 7s²

[Rn] 7s²

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹⁰ 6s² 6p⁶ 7s²

Orbital diagram

↑↓

2/2

↑↓

2/2

↑↓

6/6

↑↓

2/2

↑↓

6/6

↑↓

2/2

↑↓

10/10

↑↓

6/6

↑↓

2/2

↑↓

10/10

↑↓

6/6

↑↓

2/2

↑↓

14/14

↑↓

10/10

↑↓

6/6

↑↓

2/2

Total electrons: 88 Unpaired: 0

Atomic model

Protons 88

Neutrons 128

Electrons 88

Mass number 216

Stability Radioactive

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

No stable isotopes.

Mass number	Atomic mass (u)	Natural abundance	Half-life
206 Radioactive	206.003828 ± 0.000019	N/A	240 ms
205 Radioactive	205.006268 ± 0.000076	N/A	220 ms
216 Radioactive	216.0035334 ± 0.0000094	N/A	172 ns
231 Radioactive	231.041027 ± 0.000012	N/A	104 seconds
230 Radioactive	230.037055 ± 0.000011	N/A	93 minutes

Measured

Phase / State

Solid 25 °C (298.15 K)

Reason: 674.9 °C below melting point (699.85 °C)

Melting point 699.85 °C

Boiling point 1139.85 °C

Below melting by 674.9 °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

699.85 °C

Boiling point Literature

1139.85 °C

Current phase Calculated
Solid

Transition energies

Heat of fusion Literature

0.08291444 eV

Energy required to melt 1 mol at melting point

Heat of vaporization Literature

1.171167 eV

Energy required to vaporize 1 mol at boiling point

Heat of sublimation Literature

1.647925 eV

Energy required to sublime 1 mol at sublimation point

Density

Reference density Literature

5000 kg/m³

At standard conditions

Current density Calculated

5000 kg/m³

At standard conditions

Atomic Spectra

Showing 10 of 88 Atomic Spectra. Sorted by ion charge (ascending).

Lines Holdings ?

Ion	Charge	Total lines	Transition probabilities	Level designations
Ra I	0	143	19	112
Ra II	+1	63	9	63

NIST Lines Holdings →

Levels Holdings ?

Ion	Charge	Levels
Ra I	0	82
Ra II	+1	37
Ra III	+2	2
Ra IV	+3	2
Ra V	+4	2
Ra VI	+5	2
Ra VII	+6	2
Ra VIII	+7	2
Ra IX	+8	2
Ra X	+9	2

NIST Levels Holdings →

88 Ra 226

Radium — Atomic Orbital Visualizer

[Rn]7s2

Energy levels 2 8 18 32 18 8 2

Oxidation states +2

HOMO 7s n=7 · l=0 · m=0

Radium — Atomic Orbital Visualizer Preview

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88 Ra 226

Radium — Crystal Structure Visualizer

Crystal structure data not available

Ionic Radii

Charge	Coordination	Spin	Radius
+2	8	N/A	148 pm
+2	12	N/A	170 pm

Compounds

226.025 u

228.031 u

224.020 u

223.018 u

225.024 u

227.029 u

222.015 u

220.011 u

230.037 u

212.000 u

233.048 u

Isotopes (5)

Mass number	Atomic mass (u)	Natural abundance	Half-life	Decay mode
206 Radioactive	206.003828 ± 0.000019	N/A	240 ms	α ≈100%β+ ?
205 Radioactive	205.006268 ± 0.000076	N/A	220 ms	α ≈100%β+ ?
216 Radioactive	216.0035334 ± 0.0000094	N/A	172 ns	α =100%ε<1e-8%
231 Radioactive	231.041027 ± 0.000012	N/A	104 seconds	β- =100%
230 Radioactive	230.037055 ± 0.000011	N/A	93 minutes	β- =100%

206 Radioactive

Atomic mass (u) 206.003828 ± 0.000019

Natural abundance N/A

Half-life 240 ms

Decay mode

α ≈100%β+ ?

205 Radioactive

Atomic mass (u) 205.006268 ± 0.000076

Natural abundance N/A

Half-life 220 ms

Decay mode

α ≈100%β+ ?

216 Radioactive

Atomic mass (u) 216.0035334 ± 0.0000094

Natural abundance N/A

Half-life 172 ns

Decay mode

α =100%ε<1e-8%

231 Radioactive

Atomic mass (u) 231.041027 ± 0.000012

Natural abundance N/A

Half-life 104 seconds

Decay mode

β- =100%

230 Radioactive

Atomic mass (u) 230.037055 ± 0.000011

Natural abundance N/A

Half-life 93 minutes

Decay mode

β- =100%

Spectral Lines

Showing 50 of 90 Spectral Lines. Only spectral lines with measured intensity are shown by default.

Wavelength (nm)	Intensity	Ion stage	Type	Transition	Accuracy	Source
381.44219 nm	200	Ra II	emission	7s 2S → 7p 2P*	Measured	NIST
468.22394 nm	100	Ra II	emission	7s 2S → 7p 2P*	Measured	NIST
482.59281 nm	100	Ra I	emission	7s2 1S → 7s.7p 1P*	Measured	NIST
566.0812 nm	50	Ra I	emission	7s.6d 3D → 6d.7p 3F*	Measured	NIST
714.12167 nm	50	Ra I	emission	7s2 1S → 7s.7p 3P*	Measured	NIST
453.3111 nm	30	Ra II	emission	7p 2P* → 8s 2S	Measured	NIST
620.0304 nm	30	Ra I	emission	7s.6d 3D → 6d.7p 3F*	Measured	NIST
443.6259 nm	20	Ra II	emission	7p 2P* → 7d 2D	Measured	NIST
540.0231 nm	20	Ra I	emission	7s.6d 3D → 6d.7p 3D*	Measured	NIST
540.6796 nm	20	Ra I	emission	7s.6d 3D → 6d.7p 3D*	Measured	NIST
555.5852 nm	20	Ra I	emission	7s.7p 3P* → 7s.7d 3D	Measured	NIST
581.3628 nm	20	Ra II	emission	7p 2P* → 8s 2S	Measured	NIST
644.62 nm	20	Ra I	emission	7s.7p 3P* → 7s.7d 3D	Measured	NIST
648.7319 nm	20	Ra I	emission	7s.6d 3D → 6d.7p 3F*	Measured	NIST
698.0232 nm	20	Ra I	emission	7s.6d 3D → 6d.7p 3F*	Measured	NIST
711.8486 nm	20	Ra I	emission	7s.6d 3D → 6d.7p 3F*	Measured	NIST
722.5166 nm	20	Ra I	emission	7s.6d 1D → 6d.7p 1D*	Measured	NIST
485.6071 nm	10	Ra I	emission	7s.6d 3D → 7s.5f 3F*	Measured	NIST
485.942 nm	10	Ra II	emission	5f 2F* → 6g 2G	Measured	NIST
492.752 nm	10	Ra II	emission	5f 2F* → 6g 2G	Measured	NIST
520.5948 nm	10	Ra I	emission	7s.6d 3D → 6d.7p 3D*	Measured	NIST
528.3277 nm	10	Ra I	emission	7s.7p 3P* → 7s.7d 3D	Measured	NIST
532.029 nm	10	Ra I	emission	7s.6d 3D → 6d.7p 3D*	Measured	NIST
539.9784 nm	10	Ra I	emission	7s.6d 3D → 6d.7p 3D*	Measured	NIST
550.1985 nm	10	Ra I	emission	7s.7p 3P* → 7p2? 3P	Measured	NIST
555.3574 nm	10	Ra I	emission	7s.7p 3P* → 7s.7d 3D	Measured	NIST
561.6661 nm	10	Ra I	emission	7s.6d 3D → 6d.7p 3D*	Measured	NIST
633.6899 nm	10	Ra I	emission	7s.6d 1D → 7s.8p 1P*	Measured	NIST
659.3341 nm	10	Ra II	emission	5f 2F* → 5g 2G	Measured	NIST
671.932 nm	10	Ra II	emission	5f 2F* → 5g 2G	Measured	NIST
731.0269 nm	10	Ra I	emission	7s.7p 3P* → 7s.8s 3S	Measured	NIST
419.4091 nm	8	Ra II	emission	5f 2F* → 7g 2G	Measured	NIST
424.472 nm	8	Ra II	emission	5f 2F* → 7g 2G	Measured	NIST
464.1284 nm	8	Ra I	emission	7s.6d 3D → 7s.5f 3F*	Measured	NIST
469.9272 nm	8	Ra I	emission	7s.6d 3D → 7s.5f 3F*	Measured	NIST
548.215 nm	8	Ra I	emission	7s.6d 3D → 6d.7p 3D*	Measured	NIST
508.1036 nm	6	Ra I	emission	7s.6d 3D → 6d.7p 3P*	Measured	NIST
566.165 nm	6	Ra II	emission	8p 2P* → 9d 2D	Measured	NIST
389.455 nm	5	Ra II	emission	5f 2F* → 8g 2G	Measured	NIST
497.179 nm	5	Ra I	emission	7s.6d 3D → 6d.7p 3P*	Measured	NIST
504.154 nm	5	Ra I	emission	7s.6d 3D → 6d.7p 3P*	Measured	NIST
560.143 nm	5	Ra I	emission	7s.6d 3D → 7s.8p 3P*	Measured	NIST
577.824 nm	5	Ra I	emission	7s.6d 1D → 6d.7p 3P*	Measured	NIST
579.5745 nm	5	Ra I	emission	7s.7p 3P* → 7p2? 3P	Measured	NIST
581.1588 nm	5	Ra I	emission	7s.6d 3D → 6d.7p 1D*	Measured	NIST
616.7051 nm	5	Ra I	emission	7s.6d 3D → 6d.7p 1D*	Measured	NIST
707.79042 nm	5	Ra II	emission	6d 2D → 7p 2P*	Measured	NIST
417.798 nm	4	Ra I	emission	7s.6d 3D → 7s.6f 3F*	Measured	NIST
430.5 nm	4	Ra I	emission	7s.6d 3D → 7s.6f 3F*	Measured	NIST
490.3263 nm	4	Ra I	emission	7s.6d 3D → 6d.7p 3P*	Measured	NIST

Extended Properties

Covalent Radii (Extended)

Covalent radius (Pyykkö)

Covalent radius (Pyykkö, double)

Covalent radius (Pyykkö, triple)

Van der Waals Radii

Truhlar

UFF

MM3

Atomic & Metallic Radii

Atomic radius (Rahm)

Numbering Scales

Mendeleev

Pettifor

Glawe

Electronegativity Scales

Ghosh

Polarizability & Dispersion

Dipole polarizability

Dipole polarizability (unc.)

Phase Transitions & Allotropes

Melting point

969.15 K

Oxidation State Categories

+2 main

Advanced Reference Data

Crystal Radii Detail (2)

Charge	CN	Spin	r_crystal (pm)	Origin
2	VIII		162	from r^3 vs V plots,
2	XII		184	from r^3 vs V plots,

Isotope Decay Modes (55)

Isotope	Mode	Intensity
201	A	100%
202	A	100%
203	A	100%
203	B+	—
204	A	100%
204	B+	—
205	A	100%
205	B+	—
206	A	100%
206	B+	—

X‑ray Scattering Factors (516)

Energy (eV)	f₁	f₂
10	—	0.04162
10.1617	—	0.04479
10.3261	—	0.0482
10.4931	—	0.05188
10.6628	—	0.05584
10.8353	—	0.0601
11.0106	—	0.06468
11.1886	—	0.06961
11.3696	—	0.07492
11.5535	—	0.08102

Additional Data

Estimated Crustal Abundance

The estimated element abundance in the earth's crust.

9×10-7 milligrams per kilogram

References (1)

[5] Radium https://education.jlab.org/itselemental/ele088.html

Estimated Oceanic Abundance

The estimated element abundance in the earth's oceans.

8.9×10-11 milligrams per liter

References (1)

[5] Radium https://education.jlab.org/itselemental/ele088.html

Sources

Sources of this element.

Originally, radium was obtained from the rich pitchblende ore found in Joachimsthal, Bohemia. The carnotite sands of Colorado furnish some radium, but richer ores are found in the Republic of Zaire and the Great Lake region of Canada. Radium is present in all uranium minerals, and could be extracted, if desired, from the extensive wastes of uranium processing. Large uranium deposits are located in Ontario, New Mexico, Utah, Australia, and elsewhere.

References (1)

[6] Radium https://periodic.lanl.gov/88.shtml

References

(9)

1 PubChem

Data deposited in or computed by PubChem

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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.

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

Radium

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.

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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.

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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

Radium

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/

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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

Radium

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.

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7 NIST Physical Measurement Laboratory

Radium

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

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8 PubChem Elements

Radium

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

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9 PubChem Elements

Radium

The element property data was retrieved from publications.

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Last updated: May 1, 2026

Data verified: May 12, 2026

Content is reviewed against latest scientific data.