![]() ![]() (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.Moseley discovered that the number of protons in an element determines its atomic number.ġ919 Francis William Aston used a mass spectrograph to identify 212 isotopes.ġ922 Niels Bohr proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit.ġ923 Louis de Broglie proposed that electrons have a wave/particle duality.ġ929 Cockcroft / Walton created the first nuclear reaction, producing alpha particlesġ930 Paul Dirac proposed the existence of anti-particles.ġ932 James Chadwick discovered neutrons, particles whose mass was close to that of a proton.ġ938 Lise Meitner, Hahn, Strassman discovered nuclear fission.ġ941-51 Glenn Seaborg discovered eight transuranium elements.ġ942 Enrico Fermi created the first man-made nuclear reactor. Thomson determined the charge to mass ratio of electrons.ġ898 Rutherford discovered alpha, beta, and gamma rays in radiation.ġ898 Marie Sklodowska Curie discovered radium and polonium and coined the term radioactivity after studying the decay process of uranium and thorium.ġ900 Max Planck proposed the idea of quantization to explain how a hot, glowing object emitted light.ġ900 Frederick Soddy came up with the term “isotope” to explain the unintentional breakdown of radioactive elements.ġ903 Hantaro Nagaoka proposed an atomic model called the Saturnian Model to describe the structure of an atom.ġ904 Richard Abegg found that inert gases have a “stable electron configuration.”ġ906 Hans Geiger invented a device that could detect alpha particles.ġ914 H.G.J. Goldstein discovered canal rays, which have a positive charge equal to an electron.ġ896 Henri Becquerel discovered radiation by studying the effects of x-rays on photographic film.ġ897 J.J. Stoney theorized that electricity was comprised of negative particles he called electrons.ġ879 Sir William Crookes’ experiments with cathode-ray tubes led him to confirm the work of earlier scientists by definitively demonstrating that cathode-rays have a negative charge.ġ886 E. Plucker built one of the first cathode-ray tubes.ġ869 Dmitri Mendeleev created the periodic table.ġ873 James Clerk Maxwell proposed the theory of electromagnetism and made the connection between light and electromagnetic waves.ġ874 G.J. Democritus’ atomic theory posited that all matter is made up small indestructible units he called atoms.ġ704 Isaac Newton theorized a mechanical universe with small, solid masses in motion.ġ803 John Dalton proposed that elements consisted of atoms that were identical and had the same mass and that compounds were atoms from different elements combined together.ġ832 Michael Faraday developed the two laws of electrochemistry.ġ859 J. ![]()
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