Chapter 4 Section 1: Development of Atomic Theory
-First theory of atoms proposed over 2,000 years ago
-In 4th century B.C., Greek philosopher Democritus suggested universe was made
of invisible units that he called ATOMS
-He thought movements of atoms caused changes in matter he observed
-No evidence, though
*Dalton’s Atomic Theory (Foundation)
-1808: John Dalton (English schoolteacher)
-Said all atoms of a given element were exactly alike, & atoms of different
elements could join to form compounds
-He used experimental evidence
-Ex: Law of Definite Proportions: (A CMPD ALWAYS HAS THE
SAME FORMULA) a chemical cmpd. always contains same elements in exactly same
proportions by weight or mass (Ex: H2O)
*Goldstein
-Discovered proton
*Thomson’s Model of the Atom
-1897: J.J. Thomson (British scientist)
-Conducted cathode ray experiment: suggested cathode rays were made of
negatively charged particles that came from inside atoms (Electrons, anyone???) (Fig 3
pg. 115)
*(e-): Negatively charged particles inside atom
-Plum-pudding model (Think blueberries (e-) in a muffin) (Fig 4 pg 115)
*Rutherford’s Model of the Atom
-Ernest Rutherford (British scientist)
-Found Thomson’s model needed revised
-Rutherford proposed most of mass of atom was concentrated at atom’s center
(Nucleus, anyone???)
-Nucleus: Positively charged, dense core of the atom (Has p+ and n )
-Conducted gold-foil experiment (Fig 5 pg. 117)
*Neils Bohr Model (Danish)
-Worked in Rutherford’s lab
-Said e- move in specific orbits around nucleus
*Schrodinger’s Model
-Said e- are not particles but rather waves
*Chadwick Model
-Discovered neutron
*Heisenberg Model (Quantum model)
-Found both Bohr & Schrodinger were right
-(e-) are particles that move in a wave-like fashion