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

Proton Neutron(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)Now thought of as a the motion of

Discrete ParticlesDiscrete Particles having mass mass (Electrons)

Carrying the smallest possible unit of charge

The Plum Pudding Model

Electrons

(Negativly Charged)

J.J. Thompson- 1904

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 ?

StabilityElectrical Forces balanced by Centrifugal Forces

IdentityChange 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)----1.67 x10-24 Grams

=0.000000000000000000000001.67 Grams

1 electron-----9.1x10-28 Grams

=0.0000000000000000000000000009.1Grams

The Proton weighs 1800 x the Electron

The Atom is about 5 X 10-8 Cm

Lets Try AnalogiesIf 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 - 1935

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)

39P19

19 Protons

20 Neutrons

Atomic Mass=39

92 Protons

143 Neutrons

Atomic Mass = 235

92 Protons

146 Neutrons

Atomic Mass=238

235U92 238U92

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% U238 • 0. 7% U235 (The Bomb Type)

Problem – Not Enough 235U 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 235U based gas than 238U 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 LittleNew 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 ???

      Ti=50 Zr=90 ?=180       V=51 Nb=94 Ta=182       Cr=52 Mo=96 W=186       Mn=55 Rh=104,4 Pt=197,4       Fe=56 Ru=104,4 Ir=198       Ni=Co=59 Pd=106,6 Os=199 H=1     Cu=63,4 Ag=108 Hg=200   Be=9,4 Mg=24 Zn=65,2 Cd=112    B=11 Al=27,4 ?=68 Ur=116 Au=197?   C=12 Si=28 ?=70 Sn=118    N=14 P=31 As=75 Sb=122 Bi=210?   O=16 S=32 Se=79,4 Te=128?    F=19 Cl=35,5 Br=80 J=127  Li=7 Na=23 K=39 Rb=85,4 Cs=133 Tl=204     Ca=40 Sr=87,6 Ba=137 Pb=207     ?=45 Ce=92        ?Er=56 La=94        ?Yt=60 Di=95        ?In=75,6 Th=118?    

Mendeleev 1869

Original Table – 63 Elements

Periodic TableOf The Elements

Noble GassesAlkali Metals

Alkaline Earth

Trans

Uranic

Families

The End

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