Water is a fundamental element that cannot be decomposed into simpler substances.

Not a fact anymore

Water is a fundamental element that cannot be decomposed into simpler substances.

What we know now

Water is a chemical compound with the formula H2O. It can be formed from hydrogen and oxygen and can be decomposed into those elements.

Why it changed

Experiments in the late 18th century produced water by reacting gases and then decomposed water into hydrogen and oxygen, demonstrating through both synthesis and analysis that it was a compound.

Status: Overturned
Category: Chemistry
Accepted approximately: Classical antiquity through the 18th century
Changed approximately: 1780s

The old claim refers to the classical concept of an element, not the modern chemical definition. Ancient elemental systems were broad explanatory schemes rather than entries in a modern periodic table.

The discovery was collective. Joseph Priestley, Henry Cavendish, James Watt, Antoine Lavoisier, and others contributed observations or interpretations during the chemical revolution.

Evidence

Sources and what they establish

Historical context

Revolutionary Instruments: Lavoisier's Tools as Objets d'Art Science History Institute
Explains that water had been considered a basic element since ancient times and describes the experiments showing it was composed of hydrogen and oxygen.

Current evidence

Antoine-Laurent Lavoisier Science History Institute
States that Lavoisier proved water was composed of hydrogen and oxygen, contradicting the ancient elemental model.
Science and Celebrity: Humphry Davy's Rising Star Science History Institute
Describes electrolysis separating water into hydrogen and oxygen during early electrical experiments.