Democritus John Dalton
All elements are composed of atoms.
Atoms of the same element are identical, but different from others.
Eugen Goldstein, 1886
Atoms can physically mix together or chemically combine in simple whole­ number ratios to form compounds.
­observed a CRT and found rays traveling opposite to cathode rays
­canal rays, composed of positive particles
Chemical rxns. occur when atoms are separated, joined or rearranged. Atoms of one element are never changed into atoms of another element.
Oct 22­12:07 PM
Oct 29­8:44 PM
Thomson's Plum Pudding Model
1897 gave first hint that atoms are made of smaller particles
CRT
Passed an electric current through a gas
Released rays of negatively charged particles
http://youtu.be/niEXRLP6Q68
Oct 29­9:05 PM
Thomson concluded that the negative charges came from within the atom
negatively charged particles called "corpuscles"
Oct 29­9:12 PM
Robert Millikan 1909, calculated mass of e­
­also found quantity of charge on e­
gas was neutral, so he reasoned that there must be positively charged particles in the atom
Oct 29­9:05 PM
http://youtu.be/XMfYHag7Liw
Oct 29­8:25 PM
Rutherford's Gold Foil Experiment
(1911) Fired a stream of tiny positively charged particles at sheet of gold foil
http://youtu.be/5pZj0u_XMbc
Oct 29­9:37 PM
Conclusion...
gold atoms in the sheet of foil mostly open space, not a "plum pudding" model
Oct 29­8:39 PM
Niels Bohr
1913, electrons put into specific energy levels
electrons move in definite orbitals around nucleus
atoms have a small, dense, positively charged center,
called it the nucleus
energy of particles is quantized
Rutherford‐Bohr model
emission spectrum for hydrogen
Oct 29­9:38 PM
Oct 29­9:44 PM
Erwin Schrodinger (1926)
electrons behave like waves rather than particles
QMM ‐ Allowed energy of e‐ and probability James Chadwick, 1932
­confirmed existence of neutron
http://youtu.be/HnmEI94URK8
Oct 25­9:48 PM
Oct 29­8:58 PM
Murray Gell‐Mann
Particle physics ‐ 1969 Nobel Prize
Protons and neutrons are made of smaller particles
quarks
https://www.youtube.com/watch?v=efUUkidEgro
http://hyperphysics.phy­astr.gsu.edu/hbase/particles/quark.html
http://youtu.be/SMgi2j9Ks9k
Oct 25­9:36 PM
Oct 29­9:54 PM