Barium

About Barium

Barium is the textbook case for how solubility, not toxicity, decides whether an element is poison or pharmaceutical. Soluble Ba(2+) blocks potassium channels in cardiac muscle and is fatal at gram doses, but BaSO4 has a Ksp around 10^-10, low enough that a patient can drink 200 mL of a slurry suspension and excrete essentially all of it in a day or two. The high atomic number gives BaSO4 a mass attenuation coefficient roughly 30 times that of soft tissue at diagnostic kV, which is what makes the GI tract pop on an upper-GI series or barium enema. Outside the radiology suite, barium's flame chemistry runs the green channel in fireworks — the BaCl2-water spectrum has its strongest band around 524 nm, paired with chlorine donors like potassium perchlorate to keep the emitter intact through the burn. Drilling muds use barite to weight the column against formation pressure: roughly 80 percent of mined barite goes downhole. Then there's the YBa2Cu3O7 chemistry from the 1986-87 cuprate superconductor work, where barium's +2 ionic radius is part of why that perovskite stack happens to break the 77 K liquid-nitrogen barrier.