Atomic Theory
Claimed by: Caitlyn Caggia (ccaggia3)
Atomic theory states that matter is composed of discrete units, called atoms. The word "atom" comes from the Greek word for uncuttable, atomos. Scientists later discovered that atoms were indeed able to be broken into subatomic, or elementary, particles including protons, neutrons, and electrons. Atomic theory has evolved greatly over time, but the most recent model stems from quantum mechanics.
History
John Dalton: Law of Multiple Proportions and Atomic Mass
Main Idea Working from the conservation of mass principle, chemist John Dalton determined the law of multiple proportions to understand how different elements combined in compounds. He proposed that each element of the periodic table was composed of identical components, atoms, that were unique to each element. He also suggested that these atoms were not created nor destroyed when one element was combined with another. Dalton's empirical, experimentally-based work marked the first scientific theory of the atom. Flaws Dalton proposed a list of atomic weights in 1805. However, Dalton failed to recognize natural tendencies of elements in nature (for example, oxygen typically exists as a diatomic molecule as O_2). Dalton was unable to distinguish between atoms and molecules (groups of atoms).
Amedeo Avogadro
Main Idea
Brownian Motion
Scientists began understanding the relationships between materials and patterns began emerging in the properties of chemicals in the mid-1800's. This culminated in the periodic table, which incorporated these patterns and discoveries, was developed by Dmitri Mendeleev, a Russian chemist. In 1827, a Scottish botanist, Robert Brown, studied the motion of tiny pollen particles in water. The particles followed complex paths, dubbed Brownian Motion. As early as 1905, Albert Einstein used Brownian Motion to predict the size of atoms and molecules.
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References
Chapter 30 of OpenStax Textbook
Physics Portal page on Atomic Theory