Atomic Structure Chp 4

Philosophers “thought” about atoms Democritus -460-370 B.C. -matter made of indivisible, indestructible particles called “atoms” that can move through empty space Aristotle -384-322 B.C -matter made of earth, air, wind, and fire. No empty space -His popularity replaced Democritus’ ideas

Experiments test matter John Dalton- 1800’s -Law of Conservation of Mass Experiments -Dalton’s Atomic Theory 1. elements made of indivisible atoms 2. atoms of element are identical and different from other elements 3. atoms combine in whole # ratios 4. atoms rearrange/join in chemical reactions “Marble Model”

Experiments with Cathode Rays http://www.youtube.com/watch?v=O9Goyscbazk&feature=related Crookes-1800’s -observed cathode ray particles always bent away from the (-) side of a magnet and towards the (+) side of a magnet. -Thomson-1897 -calculated this particle's mass was 1/1840th of a hydrogen atom. He discovered the first subatomic particle called the electron.

Experiments continue with the electron https://www.youtube.com/watch?v=YhVIpf25hRQ Millikan-1910’s The Oil Drop Experiment -electrons that stuck to the oil drops had charges that varied by a common denominator of -1.602x10-19 Coulombs. -a single electron carries a charge of 1- -Millikan used the electron's charge/mass to determine the mass of an electron. -a single electron has a mass of 9.11x10-28 g.

A new model of the atom was needed Called the Plum Pudding Model -solid positive sphere -electrons scattered randomly inside -overall charge of the atom is neutral

Experiments continue with the atom http://www.youtube.com/watch?v=5pZj0u_XMbc Rutherford-1911 Gold Foil Experiment -observed alpha particles deflected at large angles. Rutherford concluded that the atom is mostly space and most of its(+) charge and mass is contained in the nucleus -Atom's are neutral due to (+) charge of the nucleus balancing the (-) charge of the electrons. -Rutherford's model could not account for all of the atom's mass

A new model of the atom was needed

More subatomic particles are discovered -Rutherford concluded in 1920 that the nucleus contained (+) particles called protons. -Chadwick concluded in 1935 that the nucleus contained another subatomic particle called the neutron. The proton and neutron are nearly equal in mass.

Particles smaller than protons, electrons, and neutrons discovered 1964-Zweig and Gell-Mann proposed quarks independently. 1968-Experiments showed quarks scattering out of colliding protons.

The Large Hadron Collider https://www.youtube.com/watch?v=83FbDC3jcmE

Dear Democritus Atomic Theory Infographic