How Was John Dalton Wrong About Molecular Theory and When Was the Chemical Composition of Water Discovered?

Many scientists who make great leaps forward in their discoveries generate as many questions as they answer, like John Dalton and his atomic theory.

Dalton had proven the existence of the atom, and his relative atomic weights were a brilliant start to measuring the atom, but questions remained.

Scientists were still puzzled by the true weight and amount of atoms that made up elements and compounds.

In 1814, the Swedish chemist Fins Berzelius calculated some atomic weights that differed from Dalton’s. Other scientists found weights different from those of both men.

Dalton thought that one atom of water was composed of one atom of hydrogen and one atom of oxygen.

He also thought that mixing one ounce of hydrogen with eight ounces of oxygen produced nine ounces of water. This would mean one ounce of hydrogen contained as many atoms as eight ounces of oxygen.

Scientists started questioning the accuracy of these ideas.

In 1809, the French chemist Joseph-Louis Gay-Lussac found that gases form compounds, like water, in simple, definite proportions of small whole numbers.

For example, he found that water actually consists of two parts hydrogen and one part oxygen.

Dalton rejected the finding because he still thought that “particles” meant only atoms.

He could not see how one particle of oxygen could produce two particles of water, but Gay-Lussac was right and Avogadro knew it.