who decided that iron was an element?

Antoine Lavoisier was the first person to organize matter into groups of elements, those materials that cannot be broken down into component parts. In his ‘Traité Élémentaire de Chimie’ published in 1789, he listed 33 distinct elements, including iron, the first time that matter had been organized in such a way.

He got a few things wrong, but ‘Traité Élémentaire de Chimie’ is still respected as the first modern textbook, and it revolutionized the field of chemistry.

Later, in 1869, Dmitri Mendeleev expanded on Lavoisier’s work and organized all known elements, then up to 63, into the modern periodic table.

Well its obvious that Iron has been known to the ancients. But no one exactly decided it was an element. Review: any substance that has an equal number of protons and electrons, and cannot be broken down into any other substance, is considerded an element. Because iron has both these properties, it is considered an element, so no one in particular decided it was an element. Its not up to people to decide whether or not something is an element, its based upon atom structure.