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Evolution of Atomic Theory: From Democritus to Niels Bohr

Discover the journey of the atom's concept from Democritus' ancient idea of indivisible particles to Niels Bohr's modern quantum model, highlighting key contributions by Dalton, Thomson, Rutherford, and others.

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Evolution of Atomic Theory: From Democritus to Niels Bohr

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Presentation Transcript

  1. History of the Atom • The beginning of time (400 BC) • Democritus stated that matter was composed of small particles called "atoms" that could be divided no further. These atoms differed by their size, shape and weight; thud resulting in different properties. Unfortunately, his ideas were largely ignored for the next 2000 years.

  2. 1803 • John Dalton stated the following • Matter is made of tiny particles called atoms • All atoms of a given element are identical • Atoms of one element are different from atoms of another • Atoms cannot be created, divided, or destroyed • Different atoms combine in whole number ratios to form compounds.

  3. 1890’s • JJ Thomson states that atoms contain a particle called the electron

  4. 1909 • Robert Millikan determined that the electron was negatively charged. • Thomson then states that atoms are made of positive “matter” with evenly distributed electrons. Creating the plum pudding model.

  5. 1911 • Ernest Rutherford • Shot alpha particles at a piece of gold foil to find that while most went straight through some where slightly thrown off course and a few bounced back. • Concluded that atoms are mostly empty space with a dense center called a nucleus

  6. 1913 • James Chadwick found the neutron in the nucleus

  7. 1932 • Niels Bohr created the quantum model of the atom that proposed electrons occupied orbitals.

  8. Today • Nucleus with protons and neutrons with an electron cloud sectioned into energy levels, shells, and subshells where electrons are located.

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