The modern atomic theory, also known as the kinetic theory of gases, was proposed by a number of scientists over the course of several centuries. However, it was not until the 19th and early 20th centuries that the theory began to take its modern form.
One of the earliest proponents of the atomic theory was the Greek philosopher Democritus, who proposed in the 5th century BCE that matter was made up of indivisible particles called atoms. However, his ideas were largely ignored by the scientific community until they were rediscovered in the 17th century by English chemist Robert Boyle. Boyle's work laid the foundation for the development of the modern atomic theory, but it was not until the 19th century that the theory began to take its current form.
In the early 19th century, British scientist John Dalton proposed a more detailed version of the atomic theory, which stated that all elements are made up of atoms, that atoms of a given element are all identical, and that chemical reactions occur when atoms are rearranged to form new molecules. This theory was widely accepted and became the basis for much of the early research on the structure of matter.
However, it was not until the late 19th and early 20th centuries that the modern atomic theory began to take shape. This was due in large part to the work of several key scientists, including English physicist J.J. Thomson, who discovered the electron, and New Zealand-born physicist Ernest Rutherford, who discovered the atomic nucleus.
In the early 20th century, Danish physicist Niels Bohr expanded upon Rutherford's work by proposing that the electrons in an atom are arranged in shells around the nucleus. This model, known as the Bohr model, was a significant step forward in the development of the modern atomic theory, as it provided a framework for understanding the behavior of electrons in an atom.
Overall, the modern atomic theory is the result of centuries of work by many different scientists, who have contributed to our understanding of the structure and behavior of matter at the atomic level. It is a fundamental concept in chemistry and physics, and continues to be an important area of study in the scientific community.