Which element was discovered in 1774 by Carl Wilhelm Scheele?

The element discovered in 1774 by Carl Wilhelm Scheele was chlorine. Scheele produced it by reacting hydrochloric acid with manganese dioxide, creating a yellow-green gas with a sharp smell and powerful bleaching properties.

Scheele called the gas “dephlogisticated muriatic acid air” and did not recognize it as a separate element. At the time, many chemists believed every acid had to contain oxygen, so chlorine was initially treated as a compound rather than a new element.

Humphry Davy later demonstrated in 1810 that the substance was an element and gave it the name chlorine, from the Greek word khlōros, meaning pale green. Chlorine has atomic number 17 and normally exists as Cl₂, a diatomic molecule.

A common mix-up is oxygen: Scheele also independently discovered oxygen, but his 1774 work on the yellow-green gas belongs to chlorine. Today, chlorine compounds are widely used in water disinfection, bleaching, and PVC manufacture, although chlorine gas itself is hazardous.