ATOMIC THEORY

ATOMIC THEORY

1. Democritus

   • His atomic theory posited that all matter is made up small indestructible units he called atoms

2. 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

3. Frederick Soddy

   • Came up with the term "isotope" to explain the unintentional breakdown of radioactive elements

4. Ernest Rutherford

   • Using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm) gold foil . He established that the nucleus was: very dense, very small and positively charged. He also assumed that the electrons were located outside the nucleus

5. G.J. Stoney

   • Proposed that electricity was made of discrete negative particles he called "electrons"

6. Niels Bohr

   • Proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit

7. Lise Meitner, Hahn, Strassman

   • Discovered neutrons, particles whose mass was close to that of a proton

8. James Chadwick

   • Discovered neutrons, particles whose mass was close to that of a proton

9. J.J. Thomson

   • Determined the charge to mass ratio of electrons. He also Studied "canal rays" and found they were associated with the proton H+