The idea that matter cannot be created or destroyed forms the foundation of modern chemistry and physics. This principle posits that the total quantity of matter remains constant despite physical or chemical changes, moving scientific thought beyond mere observation into a quantifiable system. This conservation principle remains a bedrock concept, allowing for the precise measurement and prediction of chemical reactions.
John Dalton and the Atomic Postulate
The person who explicitly stated that atoms themselves cannot be created or destroyed was the English chemist and physicist John Dalton in the early 19th century. Dalton’s atomic theory, proposed around 1803, defined the atom as the specific, indivisible particle that upheld this conservation principle. His third postulate precisely addressed this concept, declaring that atoms are indestructible particles that retain their identity during chemical changes.
Dalton explained that chemical reactions do not involve the creation or annihilation of matter, but rather the simple rearrangement of atomic units. For example, when hydrogen and oxygen combine to form water, the atoms of the elements are only separated and regrouped, with every original atom accounted for in the final product. This provided a microscopic, particulate explanation for conservation, moving the idea beyond macroscopic observation of mass.
The Preceding Concept of Mass Conservation
While Dalton provided the atomic explanation, the macroscopic idea of matter conservation was established earlier by the French chemist Antoine Lavoisier in the late 18th century. Through careful experimentation, Lavoisier formulated the Law of Conservation of Mass. This law states that in a closed system, the mass of the substances present before a chemical reaction must equal the mass of the substances after the reaction.
Lavoisier’s measurements demonstrated that mass was conserved during processes like combustion and decomposition, correcting the previous notion that matter was lost as it burned. He showed, for instance, that a metal gained mass when heated because it combined with oxygen from the air, proving that mass was accounted for, not destroyed.
However, Lavoisier’s work focused on the measurable total mass of substances, providing the experimental law but not a theoretical explanation for the existence of an underlying, conserved particle. Dalton subsequently built upon this empirical law, proposing the existence of atoms to explain why mass was conserved.
The Structure of Dalton’s Atomic Theory
Dalton’s comprehensive theory provided a full scientific context for chemistry. He proposed that all atoms of a specific element are identical to one another in both mass and properties. Conversely, atoms of different elements possess distinct masses and different properties, establishing the fundamental differences between elements.
The final key postulate explained that compounds form when atoms of different elements combine in fixed, simple whole-number ratios. This rule supported the conservation principle because combining atoms in fixed ratios ensured that the input and output of a chemical reaction would always be consistent and measurable.