About

Radium is a silvery-white, highly radioactive alkaline earth metal. It was famously used in self-luminous paints for watches and instrument dials until its severe health risks became known. Discovered by Marie and Pierre Curie, its study was pivotal in the development of radiotherapy for cancer, though it has been replaced by safer alternatives. It glows blue in the dark.

Atomic Properties

Atomic Number88

Atomic Weight226 u

Neutrons (common)138

Electron Configuration[Rn] 7s²

Full Configuration1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 7s²

Electrons per Shell2, 8, 18, 32, 18, 8, 2

Electronegativity0.9

Electron Affinity9.649 kJ/mol

Oxidation States+2

Covalent Radius221 pm

Ionic Radius148 pm

Periodic Table Position

Group2

Period7

BlockS

Chemical SeriesAlkaline earth metals

Physical Properties

State at STPsolid

Appearancesilvery-white radioactive metal

Crystal Structurebcc

Magnetic Orderingparamagnetic

Thermal Properties

Melting Point973 K

Boiling Point2,010 K

Thermal Expansion0 1/K

Thermal Conductivity18.6 W/(m·K)

Specific Heat0.094 J/(g·K)

Molar Heat21.24 J/(mol·K)

Heat of Fusion8.5 kJ/mol

Heat of Vaporization113 kJ/mol

Abundance

In Earth's Crust0 ppm

In Ocean0 ppm

In Human Body0 ppm

Discovery

Discovered byMarie Curie, Pierre Curie

Discovery Year1,898

Occurrencefrom_decay

CAS Number7440-14-4

Electron Configuration

Energy

↿⇂

1s

↿⇂

2s

↿⇂

2p

↿⇂

3s

↿⇂

3p

↿⇂

4s

↿⇂

3d

↿⇂

4p

↿⇂

5s

↿⇂

4d

↿⇂

5p

↿⇂

6s

↿⇂

4f

↿⇂

5d

↿⇂

6p

↿⇂

7s

5f

6d

7p

Isotopes of Radium

Symbol ▲	Mass (u) ▲	Abundance ▲	Half-life ▲	Decay Mode ▲
²²⁶Ra	226.025410	Trace	1600 y	Alpha Decay