In the fifth century BC, Leucippus and Democritus argued that all matter was composed of small, finite particles that they called atomos, a term derived from the Greek word for “indivisible.” They thought of atoms as moving particles that differed in shape and size, and which could join together. The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers, the scientists of their day.

Use postulates of Dalton’s atomic theory to explain the laws of definite and multiple proportions.

State the postulates of Dalton’s atomic theory.

Scientific experiments that followed Dalton were attempts to characterize how many elements there were, what the atoms of each element were like, how the atoms of each element were the same and how they differed, and, ultimately, whether there was anything smaller than an atom.By the end of this section, you will be able to: This year is considered the beginning of modern atomic theory. Dalton published his explanation in 1803. If two atoms of hydrogen always combined with one atom of oxygen, the resulting combination of atoms, called a molecule, would be water. However, his numerous and careful measurements provided the clue to another chemist named John Dalton.ĭalton realized that if elements were made up of atoms, a different atom for each different element, atomic theory could explain Lavoisier's results. Lavoisier had no explanation for these amazingly consistent results. Water could be broken down to always give exactly two volumes of hydrogen and one volume of oxygen.

For example, two volumes of hydrogen reacted exactly with one volume of oxygen to produce water. The same more complex substances he called compounds. He found two important factors: (1) the simplest substances, which he called elements, could not be broken down any further, and (2) these elements always reacted with each other in the same proportions. He reacted various substances until they were in their simplest state.

His chemical experiments involved very careful weighing of all the chemicals. One of the most famous chemists of the end of the eighteenth century was Antoine Lavoisier. They even began using the word atom again. By the seventeenth century, some of these chemists began thinking about the reactions they were seeing in terms of smallest parts.

1100) onward, many chemical reactions were studied. Aristotle's teachings against the idea of Democritus's atom were so powerful that the idea of the atom fell out of philosophical fashion for the next 2,000 years.Īlthough atomic theory was abandoned for this long period, scientific experimentation, especially in chemistry, flourished. Aristotle said there were only four elements (earth, air, fire, water) and that these had some smallest unit that made up all matter. Aristotle, one of the most influential philosophers of that time, believed in some kind of 'smallest part' of matter but not with Democritus's descriptions.

In his theory, different objects looked different because of the way the atoms were arranged. This tiniest building block that could no longer be cut he named atomos, Greek for 'no-cut.' Atomos has been changed in modern times to 'atom.' The atoms Democritus envisioned differed only in shape and size. He imagined starting with a large piece of matter and gradually cutting it into smaller and smaller pieces, finally reaching the smallest piece. One of these philosophers was named Democritus. If they could see small enough things, they would find that the same 'building blocks' they started with were still there. Still others believed that whatever comprised matter, it must be something that could not be destroyed but only recombined into new forms. Others believed that matter was made entirely of fire in everchanging forms. Some said everything was made of water, which comes in three forms (solid ice, liquid water, and gaseous steam). C., many Greek philosophers struggled to understand the nature of matter.

Aristotle atomic theory