Antoine Lavoisier
Known as 'The Father of Modern Chemistry', Antoine Lavoisier (1743-1794) made many important contributions to science. Lavoisier discovered oxygen and its role in combustion and respiration (breathing); he disproved the phlogiston theory which was popular at the time; he drew up a list of 33 elements or substances that could not be broken down further and formed the basis of the modern-day list of elements. Added to that, he proposed the Law of Conservation of Mass.
Lavoisier was born into a wealthy and aristocratic family. Hisfather was a lawyer, and in line with his family's wishes, Lavoisier completed a law degree, but his main interest was in science. In 1764, at the age of 21, he published his first paper on chemistry, and in 1768 when he was just 25 years old he was made a member of the French Academy of Sciences, one of the most important scientific institutions in the world.
Many scientists of the day were studying combustion, and the mechanisms of this process. Lavoisier, too, was fascinated by combustion and disagreed with the phlogiston theory, which he set out to disprove. He did this by carefully weighing the reacting materials and the products that were made in a chemical reaction. This was a very important step in the development of chemistry, and is now known as quantitative chemistry, that is, chemistry that involves accurate measuring. In order to accurately measure changes in mass that happened during his experiments, Lavoisier developed a balance that could weigh to 0.0()05g. Measurement was important because Lavoisier strongly believed that matter was conserved through any reaction and this belief led to the development of the Law of Conservation of Mass.
Thus it appeared that oxygen was one of the most important elements. Through this, he discovered that it did not support the phlogiston theory because after burning, the mass of the material was greater than it had been at the start. If the elements had really contained phlogiston and lost it during the reaction, they should have weighed less, not more. Further experiments were required to find out what was happening in these reactions, and Lavoisier discovered that air was absorbed as these elements burnt. He realised that something (later identified as oxygen) was taken in during combustion rather than being given out (the phlogiston theory).
The method of quantitative chemistry helped him to understand many chemical processes. One of these was that respiration was caused by chemical reactions with oxygen in the air. By carefully composing and decomposing water, he discovered that it is made up of oxygen and hydrogen. He gave names to elements which reflected their functions. For example, he came up with the name oxygen because it means acid-