MPL1203 Everything

Early Postulates What is everything (Matter)made of? Greek Mythology –Fire, Air, Water, Earth Aristotle in “Metaphysics”----- The shape and existence of all things are determined by void and atoms through the differences in shape, position and arrangement of the atoms and the proportion of void in the substance. Leucippius (Born-50BCE) Democritus (Born –460 BCE) Postulated an indivisible form of matter THE ATOM

What is An Atom Made Of? (First Approximation) Electron(s) Nucleus ProtonNeutron(s)

1897 J.J. Thompson 1899 Charge of the Electron Measured Crookes Tube Vacuum Tube Discovery of the Electron Electrons Hitting Target Electrons Missing Target

Electrons, Electricity??? Electricity was thought of as a stream, (analogous to water flowing as a pipe) Discrete Particlesmass Now thought of as a the motion of Discrete Particles having mass (Electrons) Carrying the smallest possible unit of charge

The Plum Pudding Model Electrons (Negativly Charged) J.J. Thompson Field (Positively Charged) In Today's Vernacular- The Chocolate Chip Model

Earnest Rutherford-1911 Discovery of the Nucleus Rutherford called it a“Central Charge (1920 called it a Proton)

Bohr,s Model Nucleus 1913 – Atomic Model with Fixed Orbits proposed – Modeled after the Solar System Electrons Protons Inner Orbit Outer Orbit Nucleus The Atom has No Charge Number of Protons = Number of Electrons

What Did Bohr’s Model Accomplish ? Stability Electrical Forces balanced by Centrifugal Forces Identity Change in number of Protons/Electrons Changes the Element Regeneration Once Pulled Apart, the Atom Reforms as before

How Big is It, (Are They)? 1 Proton ( or Neutron) x Grams = Grams 1 electron x Grams = Grams The Proton weighs 1800 x the Electron The Atom is about 5 X Cm

Lets Try Analogies If the Nucleus were the size of a Garbage Can The Atom would be the size of LA If an electrons weighed as much as a watermelon The proton would weigh as much as an elephant Conclusion; It’s mostly nothing

Strange Things were Happening Rutherford – 1920 Postulated a Neutron Doublet Sometimes the nucleus of an element weighed differently than another nucleus of the same element Irene and Fredrick Joliot- Curie 1932 found radiation they thought was protons James Chadwick Didn’t Believe It

James Chadwick A Unique Particle, (not an electron or a proton ) Essentially the same mass as an Proton Has no Charge With the Proton, Makes up the Nucleus Discovery of the Neutron

Bohr Model of Hydrogen and Helium

Bohr Model of Potassium(K) and Uranium (U) 39 P Protons 20 Neutrons Atomic Mass=39 92 Protons 143 Neutrons Atomic Mass = Protons 146 Neutrons Atomic Mass= U U 92

So Little From So Much Marie Curie purified 10,000,000 grams of Pitchblende to get 0.1 Grams of Uranium Natural uranium is 99. 3% U % U235 (The Bomb Type)

Problem – Not Enough 235 U How to increase the Concentration?. Combine the Uranium(s) with Fluorine to get a gas (Uranium Hexafluoride) Pass the gas through a porous filter – More 235 U based gas than 238 U gas gets through. Collect it and do it again,& again & again, & again, & again Centrifuge the Gasses- Heavier 238U based gas separates from lighter 235 U based gas Collect it and do it again,& again 7 again, & again, & again Thermal Diffusion- Used Heated, Pressurized Uranium Hexafluoride

How Big was the Job? Oak Ridge Pop. 75,000 $ 17 Billion (approx $ today)

So Much from So Little New Term—Electron Volt (ev)A Measure of Energy Chemical Reaction-Dynamite Releases 1 ev per Atom Nuclear Reaction – ( The Bomb) Releases 1,000,000 ev per atom

They like Things Orderly How we organize these different Elements??? Are there Common Characteristics ??? Mendeleev 1869 Original Table – 63 Elements

Periodic Table Of The Elements

Noble Gasses Alkali Metals Alkaline Earth Trans Uranic Families

The End

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