Describe the development of early atomic theory, including contributions from Dalton, Thomson, Rutherford, Bohr, and Schrödinger.

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Human understanding of atomic theory has developed vastly, thanks to the contributions of several scientists whose work spanned the early 1800s through the 1920s. The work of Dalton, Thomson, Rutherford, Bohr, and Schrödinger occurred over a short period, and their discoveries advanced atomic theory rapidly. Below is a brief summary of each of their contributions to atomic theory.

John Dalton
John Dalton was a scientist in the 1800s. Simply, he was the first to describe atoms and their properties. His contribution to atomic theory consisted of five main tenets (1805): 
  • All matter is composed of small particles called atoms.
  • Atoms are the smallest unit of matter; Matter cannot be broken down into units smaller than atoms; Atoms are indestructible.
  • There are different kinds of atoms; atoms of the same kind of element are identical to each other. Atoms of the same element are identical in mass and size and have the same properties.
  • In chemical reactions, atoms are rearranged, combined, or separated.
  • Compounds are formed when two or more different kinds of atoms join together.
J.J. Thomson
J.J. Thomson was a scientist who lived from the mid 19th century until the mid-20th century. Around the turn of the century, he was the first to discover sub-atomic particles: he is credited with the discovery of the electron. Thomson's discovery led to related discoveries around isotopes and radioactivity.
Ernest Rutherford
Shortly after Thomson's discovery of the electron, Ernest Rutherford discovered a concentration of mass within the center of an atom, which he called the nucleus. His famous Gold Foil Experiment in 1909 showed that atoms were composed of a nucleus surrounded by electrons. His discovery added to atomic theory by describing the atom more accurately as a conglomerate of several subatomic particles.
Niels Bohr
Niels Bohr was an active scientist around the same period as Rutherford. They worked together on a model to describe the structure of the sub-atomic particles of an atom. The Rutherford-Bohr model, or simply the Bohr model (1913), describes the atom's structure as similar to a solar system. The nucleus is in the center and smaller particles such as electrons circularly orbit around it. Bohr's model is seen as a precursor to current quantum theory.
Erwin Schrödinger
Erwin Schrödinger created several equations that advanced the understanding of atomic theory on a quantum level. Early in his career, he described the movement of an electron as a wave-function. In quantum mechanics, Schrödinger's equation (1926) is a physics description that describes quantum behavior in relation to time. Schrödinger's description of atomic structure, the wave mechanical model, describes electron position within orbitals, not orbits. This conceptualization of atomic structure posits that electrons do not orbit in circles as Bohr suggested, but rather in a much more complex manner. Schrödinger's work was at the forefront of a sea change moment in scientific history when atomic understanding was advancing into the quantum realm.

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