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This deflection could only occur if the positive components of atoms were located in a small area, which Rutherford assumed to be the center. He shot small, positively charged alpha particles at thin sheets of gold foil and noted that some particles were sharply deflected. In 1909, one of Thomson's students, Ernest Rutherford, determined that the positive charge of atoms was located in a central nucleus. (He likened the relationship of electrons to the sea of positive charge to that of plums in plum pudding.)Įrnest Rutherford: Gold Foil Experiment and the Nucleus Thus, Thomson developed the "plum-pudding" model of negatively charged electrons floating in a sea of positive charge. Thomson knew that atoms had a net neutral charge, but he only knew that negative particles existed. Thomson discovered the electron in 1897, and was the first to learn that atoms weren't actually "uncuttable" as initially thought. Thomson: The Plum-Pudding Model and Electrons Tomson's Plum-Pudding Model As early as 1905, Albert Einstein used Brownian Motion to predict the size of atoms and molecules. The particles followed complex paths, dubbed Brownian Motion. This allowed Avogadro to take more accurate atomic measurements of gases than Dalton, and differentiate atoms from molecules.Ī Scottish botanist, Robert Brown, studied the motion of tiny pollen particles in water in 1827. In 1811, Amedeo Avogadro studied gases and determined that the amount of volume a gas occupies is not determined by the mass of the gas. Dalton was unable to distinguish between atoms and molecules (groups of atoms). For example, it was Charles-Augustin de Coulomb who first determined the mathematical equation which could accurately describe the electrostatic potential between charged particles that make up an atom: Such fundamental formulas are powerful tools for helping scientists understand the interactions within and processes of both microscopic and macroscopic systems. The goal of a mathematical model is to express the underlying rules that govern atomic processes in a formula that can then predict and describe the behavior of atoms (such as is seen with the list of Bohr's mathematical models for the atom). Mathematical models of atomic processes have become more thorough and sophisticated as knowledge of atomic properties has grown. 2.8 The Current Model: Quantum Physics and Electron Orbitals.2.6 Niels Bohr: Introducing Quantum Physics.2.5 Ernest Rutherford: Gold Foil Experiment and the Nucleus.Thomson: The Plum-Pudding Model and Electrons 2.1 John Dalton: The Law of Multiple Proportions and Atomic Mass.