18th Century Chemistry

Joseph Priestley (1733-1804) Theologian, chemist, and teacher Moved to the United States because he opposed the beliefs of the Church of England Invented soda water Discovered oxygen (which he called “dephlogisticated” air) Defender of “Phlogiston” theory

Antoine Lavoisier (1743-1794) French Wealthy nobleman “Father” of modern chemistry Executed by guillotine during the French revolution

Antoine Lavoisier (1743-1794) Scientific accomplishments Helped develop the metric system Wrote the first list of elements Developed a naming system for chemical compounds Wrote the law of conservation of mass Overthrew “Phlogiston” theory

Phlogiston Theory-18th Century Science THE established theory of combustion in the 1700’s. Universities, schools, etc. all taught phlogiston theory extensively. Was overthrown in the late 1700’s by Lavoisier and others. Many thinkers died believing firmly in phlogiston theory and rejecting Lavoisier’s ideas about the so-called element “oxygen”

Phlogiston Theory Phlogiston = an element contained in flammable substances that is released when the substance is burned. Phlogisticated air = air that is completely saturated with phlogiston (flame goes out) Dephlogisticated air = air with no phlogiston in it, will cause very bright flames

Phlogiston Theory “Evidence” and explanations of phlogiston theory When you burn things, their mass gets smaller (they give off phlogiston) Plant material burns easily because plants absorb phlogiston from the air When you put a flame in an enclosed space, it burns out because the air has been saturated with phlogiston

Priestley vs. Lavoisier Joseph Priestley discovered what we now call oxygen He called it “dephlogisticated air” Antoine Lavoisier suggested that phlogiston theory was wrong He called the “dephlogisticated air” oxygen, and claimed it was a newly discovered element. He proposed that oxygen in air is what allows things to burn.

Evidence for Lavoisier’s Theory When he burned things in an enclosed space, he found that the mass did not change When some things burn, they INCREASE in mass (directly conflicts with phlogiston theory!)

Phlogiston vs. Oxygen Eventually, oxygen theory won out over phlogiston theory Priestley and many others died believing firmly in phlogiston theory and rejecting oxygen theory