Barium

Barium is an alkaline earth metal whose compounds produce brilliant green colours in fireworks and whose sulfate suspension is swallowed before X-ray examination of the stomach. Barium sulfate, completely insoluble in water, coats the gut and shows up on X-rays, despite barium being toxic in soluble forms.

• Atomic Number5656 protons, 56 electrons
• Atomic Mass137.33 u56× heavier than hydrogen
• State at Room TempSolidSolid
• Density3.62 g/cm³
• Melting / Boiling726.9°C / 1896.8°C
• Discovered1808

What is Barium?

Barium is an alkaline earth metal in Group 2 with 56 protons. More reactive than strontium, it reacts vigorously with water and quickly tarnishes in air. Barium compounds are toxic when soluble, but barium sulfate is so insoluble it passes through the body harmlessly.

Named from the Greek barys meaning heavy, because barium sulfate (baryte) is unusually dense. Carl Wilhelm Scheele identified barium oxide in baryte in 1774. Humphry Davy isolated the metal by electrolysis in 1808.

Fact Barium sulfate is so insoluble, barely 0.00024 g per litre of water, that swallowing a thick suspension of it for a stomach X-ray is completely safe, despite barium being toxic in soluble forms. The barium passes through the gut unchanged and is excreted harmlessly.

Where you find Barium

On Earth

Barium is the 14th most abundant element in the crust at approx. 500 parts per million.

• Barite (BaSO₄). The most common barium mineral, mined worldwide in enormous quantities for oil-well drilling mud.
• Witherite (BaCO₃). Barium carbonate mineral found in several countries.

How we use Barium

• Oil drilling.. Barite powder is added to drilling mud as a dense weighting agent to control reservoir pressure and prevent blowouts. Over 80% of barite production goes to this use.
• X-ray contrast.. Barium sulfate suspension swallowed before X-ray or CT imaging of the gastrointestinal tract reveals the stomach, intestines and oesophagus.
• Green fireworks.. Barium nitrate and barium chlorate produce brilliant green flames in fireworks and signal flares.
• Barium titanate.. A ferroelectric ceramic used in capacitors, ultrasound transducers, piezoelectric sensors and microphones.

Did you know? Barium titanate (BaTiO₃) was one of the first ferroelectric materials discovered (1944). It converts mechanical pressure to electrical signals and vice versa, allowing it to be used in medical ultrasound transducers, sonar, microphones and speakers. Barium titanate piezoelectric devices have become one of the most widely used smart materials in modern technology.

How it was discovered

Barium oxide was identified in baryte by Scheele in 1774. Humphry Davy isolated barium metal in 1808 using electrolysis of moist barium hydroxide, during the same remarkably productive period that he isolated calcium, strontium and magnesium.

Deeper dive: barium properties and applications

Barium titanate (BaTiO₃) is a ferroelectric material, it has a permanent electric polarisation that can be reversed by an applied electric field. This makes it a piezoelectric material that converts mechanical stress to electricity (and vice versa). Piezoelectric barium titanate crystals vibrate at ultrasound frequencies when driven by alternating current, producing the high-frequency sound waves used in medical ultrasound imaging.

Moving to 57 protons on the periodic table brings us to Lanthanum.