ELEMENTLE

Element 88 · Alkaline Earth Metal

Radium

Period 7 · Group 2

Radium is a chemical element with symbol Ra and atomic number 88. It is the sixth element in group 2 of the periodic table, also known as the alkaline earth metals. Pure radium is almost colorless, but it readily combines with nitrogen (rather than oxygen) on exposure to air, forming a black surface layer of radium nitride (Ra3N2).

Three reasons Radium stands out

  1. 1

    Radioactive, used in luminous paint.

  2. 2

    Factory workers who painted watch dials with its paint and licked their brushes suffered fatal radiation poisoning, becoming known as the Radium Girls.

  3. 3

    Before its dangers were understood, it was added to health tonics and drinking water as a supposed miraculous cure-all.

The glowing promise that became a tragedy

Radium’s intense radioactivity once inspired luminous paints, patent medicines, and reckless health claims. Dial painters who ingested it exposed the lethal consequences and transformed workplace protections. Radium behaves like calcium, so the body can deposit it in bone, where radiation damages nearby tissue.

Radium at a glance
Atomic number / protons88
SymbolRa
Family (Elementle)Alkaline Earth Metal
Classification (PubChem)Alkaline earth metal
Period7
Group2
Atomic mass (u)226.02541
Standard stateSolid
Electron configuration[Rn]7s2
Reported oxidation states+2
Electronegativity (Pauling)0.9
Atomic radius (pm)283
First ionization energy (eV)5.279
Electron affinity (eV)Not available
Density (g/cm³)5
Melting point973 K (699.85 °C)
Boiling point1413 K (1,139.85 °C)
Discovery (PubChem)1898

Values are reference data, not a specification for every temperature, pressure, or allotrope. Unknown properties are left unavailable. Superheavy-element predictions remain uncertain.

Sources & further reading

PubChem: Radium · Radium on Wikipedia

The introduction and original editorial story are adapted from Wikipedia contributors via Periodic-Table-JSON. Element descriptions and their adaptations are available under CC BY-SA 3.0. Numerical attributes use the PubChem periodic-table dataset, retrieved September 22, 2026.