In this installment on the history atom theory by physics professor (and my dad) Dean Zollman, we meet Antoine Laurent Lavoisier, the 18th century father of modern chemistry, whose observations changed the way scientists thought about matter, elements, and how constituents of matter combine. – Kim
By Dean Zollman
“The theory of atoms was inspired in the fifth century before our era by spiritual stirrings of ancient Greece in pursuit of a novel form of philosophy. For the next twenty-three centuries, it was to remain essentially a vision of the imagination. The many intellectual debates that it stirred, however important they may have appeared at the time, were primarily games of the mind.
“Not a single piece of empirical evidence, based on either observation or experimentation, existed to prove or disprove the key hypothesis of the theory – the corpuscular structure of matter.”
In the late 18th century and beyond this situation would change rapidly. Experimental studies in what we now call chemistry laid foundations upon which an atomic model of matter could be built. One important player in this experimentation was Antoine Laurent Lavoisier (1743-1794), who is considered the father of modern chemistry. Many of his observations changed the way that scientists of the latter 18th and early 19th centuries thought about matter, elements, and how constituents of matter combine.
One of his most important discoveries was the Law of Conservation of Mass. Prior to his experiments, it was thought that objects would gain or lose mass as they were heated and changed from one type of material to another. For example a common experiment was to burn sulfur. When the reaction was finished, the new material was found to have a greater mass than the sulfur that the experimenter had at the beginning. Thus, it was thought, the heating process added mass to the sulfur.
Lavoisier did experiments that were more careful than those of his predecessors. Not only did he measure the mass of the sulfur compound, but he measured the mass of the air in which it was burned. He concluded that as the sulfur changed form and gained mass, the air lost the same amount of mass as that gained by the sulfur compound. (These last sentences are a little cumbersome because I am trying to avoid modern nomenclature. Today we know that the burning of sulfur in air results in the creation of sulfur dioxide – one sulfur atom and two oxygen atoms. The gain in weight of the resulting sulfur compound occurs because of the combination of sulfur with oxygen in the air.)
He also investigated an experiment which had been reported by Joseph Priestley and others. When they mixed “inflammable air” (now called hydrogen) and oxygen, dew was produced. Thus, water was a combination of hydrogen and oxygen.
These and other experiments enabled Lavoisier to create a list of fundamental elements. Instead of air, water, fire, and earth, he created a list that included oxygen, nitrogen, hydrogen, phosphorus, zinc, sulfur, and mercury. Of course he did not get everything right; he also included light.
This list appeared in a textbook, Elements of chemistry, in a new systematic order, containing all the modern discoveries (English translation of the title). Lavoisier seemed to be on the way to showing that atoms or at least some fundamental building blocks of matter existed.
However, he was not sure. In the preface to this book he wrote, “I shall, therefore, only add upon this subject, that if, by the term elements we mean to express those simple and indivisible atoms of which matter is composed, it is extremely probable we know nothing at all about them ….” So he had discovered elements, but he was not ready to call them atoms.
In addition to being a scientist Lavoisier owed a share of a company, Ferme Generale, which collected taxes. During the French Revolution’s Reign of Terror, he and his father-in-law were arrested for his involvement in this company. They were executed by guillotine on May 8, 1794.
He was survived by his wife, Marie Anne Paulze Lavoisier, who was 13 years old when she married the 28-year-old chemist. During his life, she collaborated with him. Later she had a short, rocky marriage with the physicist Count Rumford. She did not do much to move the study of atoms forward, but she is an interesting person in the history of science. So, it is a little off task, but we will look at some of her work next time.
Images via Wikimedia Commons, public domain
Dean Zollman is university distinguished professor of physics at Kansas State University where he has been a faculty member for more than 40 years. During his career he has received four major awards — the American Association of Physics Teachers’ Oersted Medal (2014), the National Science Foundation Director’s Award for Distinguished Teacher Scholars (2004), the Carnegie Foundation for the Advancement of Teaching Doctoral University Professor of the Year (1996), and AAPT’s Robert A. Millikan Medal (1995). His present research concentrates on the teaching and learning of physics and on science teacher preparation.