Barium
Barium is a soft, silvery alkaline-earth metal that's highly reactive in its pure form but forms remarkably stable, insoluble compounds that are put to very practical use — most notably barium sulfate, which is safe enough to swallow for medical X-ray imaging even though many other barium compounds are toxic.
- Group · Period
- 2 · 6
- At room temp
- solid
- Melts at
- 1000 K
- Density
- 3.62 g/cm³
- Discovered
- 1808
Uses
Barium sulfate’s defining property — being essentially insoluble and unreactive in the body — makes it the standard “barium meal” or “barium swallow” used before X-ray and CT scans of the digestive tract, since it blocks X-rays effectively enough to outline the stomach and intestines clearly on the resulting images. The same mineral form of barium sulfate, known as barite, is also used in enormous quantities as a weighting agent in drilling fluids for oil and gas wells, where its high density helps control underground pressure.
Barium compounds are additionally used to produce the vivid green color seen in fireworks and flares, and barium-based compounds have historically been used in specialty glass and in certain rubber and paint formulations.
History
Barium compounds, particularly the mineral baryte, had been noted for unusual properties well before the element itself was isolated — Swedish chemist Carl Wilhelm Scheele recognized barium oxide as containing a new element as early as 1774. It wasn’t until 1808 that English chemist Humphry Davy successfully isolated metallic barium, using electrolysis on molten barium compounds, one of several elements he isolated this way in a short span of years. Its name comes from the Greek word barys, meaning “heavy,” a reference to the unusual density of the mineral it was first identified in.
Fun facts
- Barium sulfate is so insoluble that it can safely be swallowed as a 'barium meal' for X-ray imaging, even though soluble barium salts are poisonous.
- Barium compounds burn with a vivid green flame, which is why they're a key ingredient in green fireworks.
- Pure barium metal is so reactive with air and water that it has to be stored away from both, usually under oil or inert gas.
Frequently asked questions
If barium is toxic, why is it used for X-ray 'barium meals'?
The trick is which barium compound is used. Soluble barium compounds are genuinely poisonous because the body can absorb them, but barium sulfate is so insoluble that it passes through the digestive tract essentially untouched, coating the stomach and intestines just long enough for an X-ray to capture their shape clearly before it's excreted.
Is pure barium metal dangerous to handle?
Yes, though for different reasons than its toxic compounds — pure barium metal reacts readily with oxygen and water, tarnishing quickly in air and reacting vigorously with moisture. Because of that reactivity, it's normally stored under oil or an inert atmosphere rather than left exposed, similar to how other reactive alkaline-earth and alkali metals are handled.
Why do barium compounds turn fireworks green?
When barium atoms are heated in a flame, their electrons absorb energy and then release it again as light of a very specific color, and for barium that color falls in the green part of the spectrum. Firework makers use barium compounds specifically to produce reliable green effects, the same principle other metals use to create reds, blues and other firework colors.
Compounds
6 notable compounds containing Ba
- BaCO3mineral
Barium carbonate
A dense white powder, also found naturally as the mineral witherite, once widely used as a rodenticide because it dissolves in stomach acid but not in water.
Used for: Rat poison and ingredient in specialty ceramic glazes and optical glass
- BaCl2halide
Barium chloride
A water-soluble, toxic barium salt used in analytical chemistry to test for sulfate ions, which precipitate out as insoluble barium sulfate.
Used for: Laboratory reagent for sulfate testing and metal heat treatment
- Ba(OH)2base
Barium hydroxide
A strong alkaline base, sometimes called baryta, used in analytical chemistry to titrate weak acids because its solutions stay clear of carbonate interference.
Used for: Standard base for titrating weak organic acids in analytical chemistry
- Ba(NO3)2salt
Barium nitrate
A colorless, water-soluble oxidizer that burns with a vivid green flame, making it a mainstay of pyrotechnic formulations.
Used for: Green color agent and oxidizer in fireworks and flares
- BaSO4salt
Barium sulfate
An extremely insoluble white solid, safe to ingest despite barium's toxicity because it passes through the body unabsorbed — exactly why it works as a contrast agent.
Used for: Radiocontrast agent for gastrointestinal X-ray imaging
- YBa2Cu3O7industrial
Yttrium barium copper oxide (YBCO)
A ceramic compound famous as the first material found to superconduct above the boiling point of liquid nitrogen, opening the door to more practical high-temperature superconductor research.
Used for: High-temperature superconductor in research and superconducting wires/tapes
Isotopes
41 known isotopes
Swipe to see all columns →
| Isotope | Natural abundance | Half-life | Decay mode | Mass excess | Binding energy / nucleon | Decay width |
|---|---|---|---|---|---|---|
| Ba-130 stable | 0.11% | Stable | — | -87,256.78 keV | 8,405.51 keV | — |
| Ba-132 | 0.1% | 3.0E+21 Y | Double beta-plus decay | -88,434.9 keV | 8,409.37 keV | 4.82 × 10-45 eV |
| Ba-134 stable | 2.42% | Stable | — | -88,950 keV | 8,408.17 keV | — |
| Ba-135 stable | 6.59% | Stable | — | -87,850.66 keV | 8,397.53 keV | — |
| Ba-136 stable | 7.85% | Stable | — | -88,887.08 keV | 8,402.76 keV | — |
| Ba-137 stable | 11.23% | Stable | — | -87,721.4 keV | 8,391.83 keV | — |
| Ba-138 stable | 71.7% | Stable | — | -88,261.81 keV | 8,393.42 keV | — |
Show all 41 isotopes
| Ba-114 | — | 0.43 s | Electron capture / beta-plus decay (99.1%), ECP (20%), Alpha decay (0.9%) | -45,905.44 keV | 8,089.69 keV | 1.06 × 10-15 eV |
| Ba-115 | — | 0.45 s | Electron capture / beta-plus decay (100%), Beta-plus, proton emission (15%) | -48,920 keV | 8,116 keV | 1.01 × 10-15 eV |
| Ba-116 | — | 1.3 s | Electron capture / beta-plus decay (100%), Beta-plus, proton emission (3%) | -54,380 keV | 8,162 keV | 3.51 × 10-16 eV |
| Ba-117 | — | 1.75 s | Electron capture / beta-plus decay (100%), Beta-plus, proton emission (0%), Beta-plus, alpha emission (0%) | -57,457.91 keV | 8,187.95 keV | 2.61 × 10-16 eV |
| Ba-118 | — | 5.5 s | Electron capture / beta-plus decay (100%), ECP | -62,200 keV | 8,227 keV | 8.30 × 10-17 eV |
| Ba-119 | — | 5.4 s | Electron capture / beta-plus decay (100%), ECP (25%) | -64,590.1 keV | 8,245.93 keV | 8.45 × 10-17 eV |
| Ba-120 | — | 24 s | Electron capture / beta-plus decay (100%) | -68,888.65 keV | 8,280.29 keV | 1.90 × 10-17 eV |
| Ba-121 | — | 29.7 s | Electron capture / beta-plus decay (100%) | -70,744.85 keV | 8,293.91 keV | 1.54 × 10-17 eV |
| Ba-122 | — | 1.95 m | Electron capture / beta-plus decay (100%) | -74,608.95 keV | 8,323.76 keV | 3.90 × 10-18 eV |
| Ba-123 | — | 2.4 m | Electron capture / beta-plus decay (100%) | -75,654.96 keV | 8,330.21 keV | 3.17 × 10-18 eV |
| Ba-124 | — | 11.0 m | Electron capture / beta-plus decay (100%) | -79,089.79 keV | 8,355.82 keV | 6.91 × 10-19 eV |
| Ba-125 | — | 3.3 m | Electron capture / beta-plus decay (100%) | -79,668.98 keV | 8,358.18 keV | 2.30 × 10-18 eV |
| Ba-126 | — | 100 m | Electron capture / beta-plus decay (100%) | -82,669.91 keV | 8,379.72 keV | 7.60 × 10-20 eV |
| Ba-127 | — | 12.7 m | Electron capture / beta-plus decay (100%) | -82,817.96 keV | 8,378.46 keV | 5.99 × 10-19 eV |
| Ba-128 | — | 2.43 d | Electron capture (100%) | -85,369.16 keV | 8,395.99 keV | 2.17 × 10-21 eV |
| Ba-129 | — | 2.23 h | Electron capture / beta-plus decay (100%) | -85,060.87 keV | 8,391.08 keV | 5.68 × 10-20 eV |
| Ba-131 | — | 11.50 d | Electron capture / beta-plus decay (100%) | -86,678.96 keV | 8,398.55 keV | 4.59 × 10-22 eV |
| Ba-133 | — | 10.551 Y | Electron capture (100%) | -87,553.51 keV | 8,400.21 keV | 1.37 × 10-24 eV |
| Ba-139 | — | 82.93 m | Beta-minus decay (100%) | -84,913.92 keV | 8,367.02 keV | 9.17 × 10-20 eV |
| Ba-140 | — | 12.751 d | Beta-minus decay (100%) | -83,267.91 keV | 8,353.15 keV | 4.14 × 10-22 eV |
| Ba-141 | — | 18.27 m | Beta-minus decay (100%) | -79,732.49 keV | 8,326.08 keV | 4.16 × 10-19 eV |
| Ba-142 | — | 10.6 m | Beta-minus decay (100%) | -77,842.26 keV | 8,310.97 keV | 7.17 × 10-19 eV |
| Ba-143 | — | 14.5 s | Beta-minus decay (100%) | -73,937.21 keV | 8,281.99 keV | 3.15 × 10-17 eV |
| Ba-144 | — | 11.5 s | Beta-minus decay (100%) | -71,767.13 keV | 8,265.45 keV | 3.97 × 10-17 eV |
| Ba-145 | — | 4.31 s | Beta-minus decay (100%) | -67,516.18 keV | 8,234.8 keV | 1.06 × 10-16 eV |
| Ba-146 | — | 2.21 s | Beta-minus decay (100%) | -64,866.27 keV | 8,215.53 keV | 2.06 × 10-16 eV |
| Ba-147 | — | 0.894 s | Beta-minus decay (100%), Beta-minus, neutron emission (0.06%) | -60,264.04 keV | 8,183.24 keV | 5.10 × 10-16 eV |
| Ba-148 | — | 0.612 s | Beta-minus decay (100%), Beta-minus, neutron emission (0.4%) | -57,544.91 keV | 8,164.11 keV | 7.45 × 10-16 eV |
| Ba-149 | — | 352 ms | Beta-minus decay (100%), Beta-minus, neutron emission (2.2%) | -52,830.62 keV | 8,131.85 keV | 1.30 × 10-15 eV |
| Ba-150 | — | 0.259 s | Beta-minus decay (100%), Beta-minus, neutron emission | -49,889.8 keV | 8,111.84 keV | 1.76 × 10-15 eV |
| Ba-151 | — | 0.167 s | Beta-minus decay (100%), Beta-minus, neutron emission | -44,940 keV | 8,079 keV | 2.73 × 10-15 eV |
| Ba-152 | — | 0.139 s | Beta-minus decay (100%), Beta-minus, neutron emission | -41,610 keV | 8,057 keV | 3.28 × 10-15 eV |
| Ba-153 | — | 0.116 s | Beta-minus decay (100%), Beta-minus, neutron emission | -36,470 keV | 8,023 keV | 3.93 × 10-15 eV |
| Ba-154 | — | 53 ms | Beta-minus decay (100%), Beta-minus, neutron emission | -32,920 keV | 8,001 keV | 8.61 × 10-15 eV |