Pioneering discoveries that became turning points in the history of chemistry.
British educator and philosopher Joseph Priestley (1733 – 1804) discovered oxygen in experiments, isolated the gas, and described its function in combustion and respiration. He also invented soda or carbonated water by dissolving fixed air with water. Unaware of the significance of his discoveries and because of his stubborn refusal to abandon the phlogiston theory, he named the new gas “dephlogisticated air.” However, it would be the French chemist Antoine Lavoisier (1743 – 1794) who gave the gas its present name, and was able to explain the nature of the element, accurately describing its role in combustion that totally discredit the phlogiston theory. In addition, Lavoisier collaborated with others to develop a systematic chemical nomenclature that facilitates dialogue among chemists and is still very much in use today.
John Dalton (1766 – 1844), English chemist and physicist, proposed the atomic theory, which states that: a.) all elements are made up of tiny particles called atoms; b.) all atoms of an element are identical; c.) the atoms of dissimilar elements can be distinguished from one another by their corresponding relative weights; d.) atoms of an element can be combined with atoms of another elements to form chemical compounds; and e.) atoms cannot be created, broken down into smaller particles, nor destroyed in a chemical process. He also presented a way of associating invisible atoms with quantifiable amounts such as mass of a mineral or volume of a gas. Dalton’s theory has undergone modifications through the centuries, but it has as much significance for the future of the science as Lavoisier’s oxygen-based chemistry had been.
Molecules are Made Up of Atoms (1810s – )
At a time when the words “atom” and “molecule” were used interchangeably, Italian scientist Amedeo Avogadro (1776 – 1856) clarified that atoms combine to form molecules; and proposed his eponymous principle which asserts that “Equal volumes of ideal gases, at the same conditions of temperature and pressure, contain equal numbers of particles or molecules.”