Barium
Element 56 · Alkaline Earth Metal
Barium is a classic group 2 metal: it readily loses its two outer electrons to form Ba2+ ions and reacts with water and oxygen, so it is always found combined in minerals. Its name comes from the Greek barys, meaning heavy, a nod to the density of its ores.
Most people meet barium indirectly. Barium sulfate is swallowed or injected as a contrast agent for X-rays of the gut, and barium nitrate gives fireworks their vivid green. Because soluble barium compounds are toxic, the insoluble sulfate is the form used safely in medicine.
Key facts
| Atomic number | 56 |
|---|---|
| Atomic weight | 137.33 |
| Category | Alkaline Earth Metal |
| Group / Period | 2 / 6 |
| Block | s |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 |
| Common oxidation states | +2 |
| State at STP | Solid |
| Electronegativity | 0.89 |
| Density | 3.51 g/cm³ |
| Melting point | 727 °C |
| Boiling point | 1897 °C |
Occurrence
Barium occurs as the minerals barite (barium sulfate) and witherite (barium carbonate). Barite is mined in large quantities as a weighting agent for drilling fluids.
Applications
X-ray contrast agent (barium sulfate)
Green color in fireworks and flares
Getter material in vacuum tubes
Weighting agent in oil-well drilling muds
Common compounds
- barium sulfate
- barium carbonate
- barium chloride
- barium nitrate
Barium sulfate is opaque to X-rays yet so insoluble that it passes through the body unabsorbed — which is why it can be safely swallowed for medical imaging.
Data source: IUPAC standard atomic weights 2021