Key Points

● The ancient Greek philosophers Democritus and Leucippus recorded the concept of the atomos, an indivisible building block of matter, as early as the 5th century BCE.

● The idea of an indivisible particle was further elaborated upon and explored by a number of scientists and philosophers, including Galileo, Newton, Boyle, Lavoisier, and Dalton.

● John Dalton, an English chemist, and meteorologist are credited with the first modern atomic theory based on his experiments with atmospheric gases.

Terms

atoms - smallest possible amount of matter that still retains its identity as a chemical element, now known to consist of a nucleus surrounded by electrons

law of multiple proportions law - stating that reactants will always combine in set whole number ratios.

Early History of the Atom

The matter is composed of indivisible building blocks. This idea was recorded as early as the fifth century BCE by Leucippus and Democritus. The Greeks called these particles atomos, meaning indivisible, and the modern word “atom” is derived from this term. Democritus proposed that different types and combinations of these particles were responsible for the various forms of matter. However, these ideas were largely ignored at the time, as most philosophers favored the Aristotelian perspective.

The concept of the atom was revisited and elaborated upon by many scientists and philosophers, including Galileo, Newton, Boyle, and Lavoisier. In 1661, Boyle presented a discussion of atoms in his The Sceptical Chymist. However, the English chemist and meteorologist John Dalton are credited with the first modern atomic theory, as explained in his A New System of Chemical Philosophy.

John Dalton’s A New System of Chemical Philosophy

Chemical structures from Dalton’s A New System of Chemical Philosophy.

Dalton’s experiments with gases led to some of the earliest measurements of atomic masses and a concept of atomic structure and reactivity. Dalton’s atomic theory contained the following ideas:

● All atoms of a given element are identical.

● The atoms of different elements vary in mass and size.

● Atoms are indestructible.

● Chemical reactions may result in their rearrangement, but not their creation or destruction.

Dalton also outlined a law of multiple proportions, which described how reactants will combine in set ratios. Like the early philosophers, Dalton’s theories were not popularly accepted for much of the 19th century, but his ideas have since been accepted, with amendments addressing subatomic particles and the interconversion of energy and mass.

https://courses.lumenlearning.com/introchem/chapter/early-ideas-about-atoms/

Democritus and the Greek Philosophers

About 2,500 years ago, early Greek philosophers believed the entire universe was a single, huge, entity. In other words, "everything was one." They believed that all objects, all matter, and all substances were connected as a single, big, unchangeable "thing." One of the first people to propose "atoms" was a man known as Democritus. As an alternative to the beliefs of the Greek philosophers, he suggested that atomos, or atomon - tiny, indivisible, solid objects - make up all matter in the universe.

Democritus then reasoned that changes occur when the many atomos in an object were reconnected or recombined in different ways. Democritus even extended this theory, suggesting that there were different varieties of atomos with different shapes, sizes, and masses. He thought, however, that shape, size, and mass were the only properties differentiating the different types of atomos. According to Democritus, other characteristics, like color and taste, did not reflect properties of the atomos themselves, but rather, resulted from the different ways in which the atomos were combined and connected to one another.

The early Greek philosophers tried to understand the nature of the world through reason and logic, but not through experiment and observation. As a result, they had some very interesting ideas, but they felt no need to justify their ideas based on life experiences. In a lot of ways, you can think of the Greek philosophers as being "all thought and no action." It's truly amazing how much they achieved using their minds, but because they never performed any experiments, they missed or rejected a lot of discoveries that they could have made otherwise. Greek philosophers dismissed Democritus' theory entirely. Sadly, it took over two millennia before the theory of atomos (or "atoms," as they're known today) was fully appreciated.

Summary

2,500 years ago, Democritus suggested that all matter in the universe was made up of tiny, indivisible, solid objects he called "atomos." However, other Greek philosophers disliked Democritus' "atomos" theory because they felt it was illogical.

https://chem.libretexts.org/Courses/Sacramento_City_College/SCC%3A_CHEM_330_-_Adventures_in_Chemistry_(Alviar-Agnew)/02%3A_Atoms/2.01%3A_Atoms_-_Ideas_from_the_Ancient_Greeks