Radium (Ra)

Radium is a radioactive chemical element with the atomic number 88 in the periodic table. It’s the 84th most abundant substance found in Earth’s crust with an occurrence of about one part per trillion by weight. 

Being a member of the alkaline earth metals family of periodic table elements, this extremely rare metal has two valence electrons which makes it an unstable element whose radionuclides undergo several stages of radioactive decay until the final decay element is lead. The element 88 also possesses both high luminosity and intense radioactivity as the two main characteristics of radium. 

Chemical and Physical Properties of Radium

The symbol in the periodic table of elementsRa
Atomic number88
Atomic weight (mass)226.0254 g.mol-1
Group number2 (IIA)
ColorA brilliant silvery-white radioactive metal
Physical stateSolid metal at room temperature
Half-lifeFrom 2.6(21) milliseconds [0.7(+33−3) milliseconds] to 1600 years
Electronegativity according to Pauling0.9
Density5 g. cm-3
Melting point696°C, 1285°F, 969 K
Boiling point1500°C, 2732°F, 1773 K
Van der Waals radius0.230 nm
Ionic radiusUnknown
Most characteristic isotope226Ra
Electronic shell[Rn] 7s2
The energy of the first ionization509.1 kJ.mol-1
The energy of the second ionization975 kJ.mol-1
Discovery dateIn 1898 by Marie Sklodowska (Marie Curie) and Pierre Curie

With the periodic table symbol Ra, atomic number 88, atomic mass of 226.0254 g.mol-1, and electron configuration [Rn] 7s2, pure radium is a silvery-white soft metal. It reaches its boiling point at 1500°C, 2732°F, 1773 K, while the melting point is achieved at 696°C, 1285°F, 969 K. This highly radioactive substance has an electronegativity of 0.9 according to Pauling, whereas the atomic radius according to van der Waals is 0.230 nm. 

Radium is a member of the alkali metals family of the periodic table, along with the elements beryllium, magnesium, calcium, strontium, and barium. The element 88 emits alpha particles, beta particles, gamma rays, beta rays, and alpha rays of high radioactive energy. It has a body-centered cubic crystal structure and does not possess any magnetic properties. 

When exposed to air, the silvery-white radium metal tarnishes to black due to nitride formation occurring as a result of radium’s reaction with nitrogen. On the other hand, when exposed to flame, this alkali earth metal burns with a red-colored fire. The light rays emitted by radium typically have a light-blue to green glow.

How Was Radium Discovered?

In their Paris laboratory, the two highly respected scientists Marie Curie (1867-1934) and Pierre Curie (1859-1906) were studying a complex mineral sample obtained from North Bohemia that contained uranium. This mineral was labeled as pitchblende, also known as uraninite, which was formed by oxidation of the chemical element uranium. 

Used as a coloring agent, the residue of this substance was regularly deposited in the nearby forests. Polish physicist and chemist Marie Curie observed that this waste has a devastating effect upon the surroundings, which made her believe there is an undiscovered radioactive substance in the mineral compound, even stronger than uranium. 

In 1898, Marie and Pierre managed to process tones of pitchblende slag in order to trace the new element that emits strong radiation. In order to produce one-seventh of a gram of radium, the Curie Spouses needed at least one tone of pitchblende. Their dedicated efforts resulted in the discovery of the intensely radioactive element 88 – radium. 

By conducting electrolysis of radium chloride, the pure metallic form of radium was first isolated in 1910 by Marie Curie and the French chemist André-Louis Debierne.  

Marie Curie’s Legacy to the World of Science

The Mother of modern physics and the first researcher of radioactivity, Marie Curie, discovered radium together with her husband Pierre Curie – a highly respected industrial scientist, inventor, and one of the founders of modern physics. This monumental discovery of these great chemists follows after years full of passion for science.

During those years spent in utter dedication to chemistry, Pierre and Marie Curie made many other significant discoveries. 

To begin with, Maria Skłodowska (Marie Curie) was the first woman professor at the Sorbonne, and the first woman awarded a Ph.D. in research science in Europe. This great Polish-born scientist was also the first woman to be awarded a Nobel Prize, as well as the first person to win Nobel Prizes in two different scientific disciplines – physics (in 1903) and chemistry (in 1911). 

Marie Curie shared her Nobel Prize in physic with her husband Pierre Curie and their colleague Henri Becquerel for the pioneering work in radioactivity, while the second Nobel Prize in Chemistry was awarded to both her and Piere for discovering the chemical elements polonium and radium while studying radioactivity. 

Marie Curie’s Work on Radioactivity

Radium was not the only discovery that Marie had made. She also discovered the element polonium and coined the word ‘radioactivity’ during her research on this phenomenon. Marie and Pierre defined radioactivity as a property of a chemical element with a high atomic mass, produced by radioactive elements such as uranium, thorium, polonium, and radium. 

Inspired by the work of Henri Becquerel on uranium, Marie Curie conducted a series of research on the “Becquerel rays” (i.e. rays emitted by uranium that could pass through a metal) in order to trace this property in other chemical elements. Thorium was the first substance in which she detected radioactivity, but then she observed that radioactivity is a property of the internal electron arrangement within the atom, i.e. an atomic property, rather than a molecular arrangement. 

Also, by using the electrometer invented by Pierre and his brother, Marie observed that the uranium rays electrically charge the air when they pass through it and that thorium emits rays in the same way as uranium. Finally, she concluded the rays were not a result of a chemical reaction, but rather that they came from within the uranium atoms. 

Still, her scientific curiosity didn’t stop there. From this point on, she continued with the development of the X-radiography. Unfortunately, the high radioactivity of radium took its toll. After only a few months of discovering it, Marie Curie passed away from aplastic anemia, a type of cancer developed as a result of overexposure to the dangerous radiation on the intensely radioactive substance. 

Today, the Curie Institutes founded by Marie Curie are important medical research centers, while the office and laboratory in the Curie Pavilion of the Radium Institute are now known as the Curie Museum.

How Did Radium Get Its Name?

Radium’s name originates from the Latin word “radius” which means “a ray”. It was named after the luminescent rays that were emitted from this radioactive element. 

Where Can You Find Radium?

Being extremely reactive, radium is almost never found in its pure, elemental form in nature. The naturally occurring radium is mainly found in phosphate rocks, thorium ore, or uranium ore, but traces of this highly radioactive chemical element can also be found in soil, groundwaters, various rock formations, plants, and even animals. Mainly, radium occurs in a form of radium bromide and chloride as a byproduct of uranium mining.

The process of industrial radium extraction first commenced in the 20th century. Canada, Congo,  Belgium, Slovakia, and the United Kingdom are the world’s leading countries in radium production. Congo and Canada also count as the locations where most of the uranium mines are located from which radium is obtained.

Radium in Everyday Life

Due to its extremely high and dangerous radioactivity, radium has very few uses today. However, before the dangerous effects of radiation were discovered, radium was mainly used for its luminescent properties in the form of radium bromide. 

Namely, in the early days after the discovery of the element 88, it was used in self-luminous paints applied to objects that could use an added visibility and glow in the dark, such as aircraft switches, in clock and watch dials. In this way, it was easier for people to see them in low light or complete darkness at night. 

Radium was also used in the manufacturing of toothpaste, hair creams, and other everyday products. But, when it was noticed that people who have been exposed to radium enriched paint frequently fall ill of anemia, sores, and bone cancer, the radium was banned to be used in everyday products. In 1924, a New York doctor observed signs of jaw cancer in a large number of young women who worked with self-luminous paint applied on instrument dials, later recognized as “the Radium Girls”.

The most dangerous health effects were observed in the radium dial painters who tipped their paintbrushes with their lips during painting. In this way, they were directly absorbing copious amounts of radium via the mouth. Unfortunately, the most famous victim of the highly toxic and dangerous effects of this intensely radioactive substance was its discoverer, Marie Curie. 

Despite having no commercial uses, radium has two significant applications in everyday life in nuclear medicine. Namely, the radon gas produced from radium chloride is used in radiotherapy as a part of cancer treatments. 

Furthermore, radium is used to produce neutron sources, as well as in scientific research and X-ray experiments. In 1909, the “father of nuclear physics”, Ernest Rutherford, used radium as a source of alpha particles in a helium nucleus.

How Dangerous Is Radium?

This highly radioactive chemical element is classified as one of the strongest carcinogenic substances, according to the EPA. The radioactivity of radium, just like of any other radioactive element, triggers mutation of the cell’s mechanisms of the body which leads to the formation of tumorous growth and bone marrow degradation. Most frequently, exposure to the intense radioactivity of radium leads to bone cancer and prostate cancer, cataracts, anemia, etc.

Environmental Effects of Radium

High levels of this naturally occurring chemical element can be found in the areas where radium processing facilities are located. The radon gas as a byproduct of radium is one of the greatest air pollutants which can be found in the basements, buildings, and rooms we reside in. Typically, the radium-226 isotope decays into radon-222 decays, i.e. radon gas.

The Radon Gas

According to the United States Environmental Protection Agency (EPA), radon gas is a naturally-occurring colorless and odorless radioactive gas. This noble gas is a byproduct of an intermediate decay of radium that occurs in the mineral rocks and soil that also contain other radioactive elements. After smoking tobacco, radon gas is considered to be the second leading cause of lung cancer in the United States.

Isotopes of Radium

Radium is part of a long decay chain where it slowly decays into radon, then into polonium, and into lead at the end of the process. As they decay, the isotopes of this highly radioactive chemical element emit a pale blue phosphorescent glow in the dark. 

The radium-226 isotope is both the most abundant and the longest living form of radium. In addition, there are no stable isotopes of radium. 


[n 1]



ZNIsotopic mass (Da)

[n 2][n 3]



[n 4]



[n 5]

Spin and


[n 6][n 7]



Excitation energy[n 7]
202Ra 88114202.00989(7)2.6(21) ms

[0.7(+33−3) ms]

203Ra 88115203.00927(9)4(3) msα199Rn(3/2−) 
β+ (rare)203Fr
204Ra 88116204.006500(17)60(11) ms

[59(+12−9) ms]

α (99.7%)200Rn0+ 
β+ (.3%)204Fr
205Ra 88117205.00627(9)220(40) ms

[210(+60−40) ms]

β+ (rare)205Fr
206Ra 88118206.003827(19)0.24(2) sα202Rn0+ 
207Ra 88119207.00380(6)1.3(2) sα (90%)203Rn(5/2−, 3/2−) 
β+ (10%)207Fr
208Ra 88120208.001840(17)1.3(2) sα (95%)204Rn0+ 
β+ (5%)208Fr
209Ra 88121209.00199(5)4.6(2) sα (90%)205Rn5/2− 
β+ (10%)209Fr
210Ra 88122210.000495(16)3.7(2) sα (96%)206Rn0+ 
β+ (4%)210Fr
211Ra 88123211.000898(28)13(2) sα (97%)207Rn5/2(−) 
β+ (3%)211Fr
212Ra 88124211.999794(12)13.0(2) sα (85%)208Rn0+ 
β+ (15%)212Fr
213Ra 88125213.000384(22)2.74(6) minα (80%)209Rn1/2− 
β+ (20%)213Fr
214Ra 88126214.000108(10)2.46(3) sα (99.94%)210Rn0+ 
β+ (.06%)214Fr
215Ra 88127215.002720(8)1.55(7) msα211Rn(9/2+)# 
216Ra 88128216.003533(9)182(10) nsα212Rn0+ 
EC (1×10−8%)216Fr
217Ra 88129217.006320(9)1.63(17) μsα213Rn(9/2+) 
218Ra 88130218.007140(12)25.2(3) μsα214Rn0+ 
β+β+ (rare)218Rn
219Ra 88131219.010085(9)10(3) msα215Rn(7/2)+ 
220Ra 88132220.011028(10)17.9(14) msα216Rn0+ 
221Ra 88133221.013917(5)28(2) sα217Rn5/2+Trace[n 8]
CD (1.2×10−10%)207Pb


222Ra 88134222.015375(5)38.0(5) sα218Rn0+ 
CD (3×10−8%)208Pb


223Ra[n 9]Actinium X88135223.0185022(27)11.43(5) dα219Rn3/2+Trace[n 10]
CD (6.4×10−8%)209Pb


224RaThorium X88136224.0202118(24)3.6319(23) dα220Rn0+Trace[n 11]
CD (4.3×10−9%)210Pb


225Ra 88137225.023612(3)14.9(2) dβ225Ac1/2+Trace[n 12]
226RaRadium[n 13]88138226.0254098(25)1600(7) yα222Rn0+Trace[n 14]
ββ (rare)226Th
CD (2.6×10−9%)212Pb


227Ra 88139227.0291778(25)42.2(5) minβ227Ac3/2+ 
228RaMesothorium 188140228.0310703(26)5.75(3) yβ228Ac0+Trace[n 11]
229Ra 88141229.034958(20)4.0(2) minβ229Ac5/2(+) 
230Ra 88142230.037056(13)93(2) minβ230Ac0+ 
231Ra 88143231.04122(32)#103(3) sβ231Ac(5/2+) 
232Ra 88144232.04364(30)#250(50) sβ232Ac0+ 
233Ra 88145233.04806(50)#30(5) sβ233Ac1/2+# 
234Ra 88146234.05070(53)#30(10) sβ234Ac0+ 

Source: Wikipedia

List of Radium Compounds

Being an alkaline earth metal, radium also adopts an oxidation state of +2 like the other members of the periodic system family. This makes element 88 extremely reactive. 

The radium metal decomposes in water, thus forming the radium hydroxide compound as well as hydrogen gas. Upon exposure to air, radium readily reacts with nitrogen. A black surface layer of radium nitride results from this chemical reaction. 

The radium compounds which are difficult to be solved often co-precipitate with all barium, most strontium, and most lead compounds.

  • Radium Nitride
  • Radium Hydroxide
  • Radium Nitrate
  • Radium Sulfide
  • Radium Sulfate
  • Radium Chloride
  • Radium Acetate
  • Radium Fluoride
  • Radium Bromide
  • Radium Oxide
  • Radium Phosphate
  • Radium Chloride Dihydrate
  • Radium Sulfite
  • Radium Iodide
  • Radium Polonide
  • Radium Chlorate
  • Radium Phosphide
  • Radium Carbonate
  • Radium Chlorite
  • Radium Oxalate
  • Radium Dihydrogen Phosphate
  • Radium Perchlorate
  • Radium Salts
  • Radium Iodite
  • Radium Permanganate
  • Radium Phosphite
  • Radium Bromate
  • Radium Nitrite
  • Radium Dichromate
  • Radium Bromite
  • Radium Perfluorate
  • Radium Perbromate

5 Interesting Facts and Explanations

  1. Marie Curie is the only scientist whose work has been honored with Nobel Prizes in both physics and chemistry.
  2. Radium is both the most volatile and the heaviest chemical element of the alkaline-earth family in the periodic table. In addition, it’s the first radioactive element that has been synthetically produced. 
  3. Due to its luminescence, radium was labeled as the ‘wonder element’ long before the dangerous effects of radiation were recognized by scientists.
  4. Radium’s radiation is more than one million times stronger than uranium’s radiation. Becquerel is the measuring unit of the radium’s radioactivity. 
  5. All uranium minerals contain radium.