lec2 - 9/2/08 atoms-molecules-substances how do we now...

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9/2/08 atoms-molecules-substances how do we now atoms exist? Scanning tunneling microscope-no light. Uses electron properties. Shows individual atoms. Ostwald didn't believe in atoms “accounting system” but not real mechanical objects. Changed his mind in 1906 after Avogadro's number and Einstein. Dalton's theory said nothing about structure of atom electrical charge-positive”+” and negative”-” electrical forces-two positive objects will repel each other, same with 2 neg. opposite are attracted. Coulomb's Law: 2 objects r distance apart. force=constant x q1q2/r2 positive force increases distance, negative is attractive. Magnetic force-only acts on moving charge see fig. 2.5 3 famous experiments (around 1900) Thomson's Expt. (1897)-cathode rays (aka electrons) voltage-something went through it (fig. 2.6) what is happening? Thomson determined that it has a neg. charge bends in way you would expect neg. Particles to Force balance-elec. Force up and mag. Force down. If make them equal, ray goes right through.
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lec2 - 9/2/08 atoms-molecules-substances how do we now...

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