Radium (Ra)

Isotopes of Radium

Isotope Atomic Mass Half-life Mode of Decay Nuclear Spin Nuclear Magnetic Moment
Ra-223 223.018497 11.435 days α to Rn-219; C-14 3/2 0.271
Ra-224 224.020202 3.66 days α to Rn-220; C-12 0 No data available 
Ra-225 225.023603 14.90 days β- to Ac-225 3/2 -0.734
Ra-226 226.025403 1599 years α to Rn-222; C-14 0 No data available 
Ra-227 227.029170 42 minutes β- to Ac-227 3/2 -0.404
Ra-228 228.031063 5.76 years β- to Ac-228 0 No data available 


Radium was discovered in 1898 by Pierre and Marie Curie. It takes its name from the Latin word radius, meaning “ray.”

The chemistry of radium is very similar to that of barium. The metal forms a number of salts in its +2 valence state, the only valence state typical of alkaline earth metals. The few salts that are of commercial use include chloride (RaCl2), bromide (RaBr2) and sulfate (RaSO4).

Radium was once an additive in products such as toothpaste, hair creams and even food items, due to its supposed curative powers. Such products soon were prohibited by authorities in many countries after it was discovered they could have serious adverse health effects. Mixed with phosphors in minute proportion, radium has also been used to make luminous paints and watch dials — these uses were discontinued in the 1960s.

Radium salts have several applications. Used historically in cancer treatment for destroying malignant tumors, they have been replaced by more readily available and low-cost radioisotopes such as Cobalt-60. Radium's gamma radiation is used for irradiating metals to detect fractures in welding. Radium-226 is a source material for producing Radon-222 in radiotherapy treatments (Radon-222 is safer to use because of its much shorter half-life of 3.8 days).

The radiation from radium can cause lung cancer, osteogenic sarcoma, blood dyscrasias and injury to skin. Inhalation, ingestion, skin contact or bodily exposure to radium or any of its salts must be avoided.

Properties of Radium

Name Radium
Symbol Ra
Atomic number 88
Atomic weight 226
Standard state Solid at 298 °K
CAS Registry ID 7440-14-4
Group in periodic table 2
Group name Alkaline earth metal
Period in periodic table 7
Block in periodic table s-block
Color Metallic
Classification Metallic
Melting point 700 °C
Boiling point 1737 °C
Thermal conductivity 19 W/(m·K)
Electrical resistivity 100 x 10-8 Ω·m
Electronegativity 0.9
Heat of vaporization About 125 kJ·mol-1
Heat of fusion About 8 kJ·mol-1
Density of solid 5.00 g/cm3
Electron configuration [Rn]7s2
Oxidation state  +2

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