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Period: 100 to
Philosophical Atomism
Starting around the fifth century BC, several Indo-European scholars theorized on the idea of Atomism, that all matter was made up of various indivisible particles. It fell out of prominence for close to a milenium, but then had a resurgence in popularity in the eighteenth century, shortly before the modern scientific theory of the atom was developed. -
Optics and Moving Particles
In 1666, Isaac Newton experimented with the refraction of light, proving that spectral colour was an inherient property of light. While only tangentally related to atomic theory in and of itself, this would lay the groundwork for scientists later. Although he was unable to provide direct proof for an atomic theory, Newton was a stauch supporter of both atomism and a mechniastic view of the universe, and this influenced his work and likely the work of later scientists. -
Waves versus Particles
In the late sixteen hundreds, Christiaan Huygens introduced the wave theory of light, which, although imperfect, furthered our understanding and provided a framework for later discoveries. -
Period: to
Dalton's Model
Extrapolating from the recently discovered physical laws regarding the conservation of matter and the existance of definite proportions of chemical reactions, John Dalton realized that an atomist model could easily describe these laws, as discrete particles of matter interacted, and theorized that each element was made up of very small, indivisible atoms with particular properties. -
Spectroscopy
Gustav Kirchhoff formulated three laws of spectroscopy, which would later provide the foundation for the study of black body radiation and our maodern understanding of atomic structure. -
Unification of Light, Electricity, and Magnetism
In the late eighteen hundreds, James Clerk Maxwell began work on the subject of electromagnetism, eventually theorizing that light was an electromagnetic phenominon, indirectly providing the basis for our modern understanding of spectral emissions, and by extension, the structure of the atom. -
Proof of Concept
Working his doctoral dissertation, Heirnich Hertz proved empirically Maxwell's theory of light, allowing for quantum theory to be formulated and further our understanding of hte atom. -
Quantum Theory
In the late ninteenth century, Max Planck began to work on the problem of blackbody radiation, and in doing so, founded quantum mechnaics, the model Neils Bohr would use to complete the current picture of the atom. -
Period: to
Thompson's Model
While working with cathode rays, J. J. Thompson discovered another particle, negatively charged and far smaller than the atom. This lead him to theorize that these particles (later named electrons) were the building blocks of atoms, and were distributed through a positive charge. -
Brownian Motion
In 1905, Albert Einstein published a paper showing that Brownian motion (the random movement of small particles suspended in a liquid or gas) was empirical proof for an atomic theory of matter. Later, he also expanded on the work of Max Planck, further defiing quantum theory. -
Period: to
Rutherford's Model
Not long after Thompson's discovery, one of his students, Ernest Rutherford, proved him wrong. In an expreiment where highly charged particles were shot at a metal sheet; from the amound of deflection measured, it was clear that atoms had, in addition to electrons, a very small, and strongely positive nucleus. -
Period: to
Electron Shells
The last remaining problem in the theory of the atom (orbital decay of electrons) was solved by Neils Bohr who applied quantum theory to the atom and showed that they could only orbit at distinct energy levels.
