Transcript Document

Everything
MPL1203
Early Postulates
What is everything (Matter)made of?
Greek Mythology –Fire, Air, Water, Earth
Leucippius (Born-50BCE)
Democritus (Born –460 BCE)
Postulated an indivisible form of matter
THE ATOM
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.
What is An Atom Made Of?
(First Approximation)
Electron(s)
Nucleus
Proton
Neutron(s)
Discovery of the Electron
1897 J.J. Thompson
1899 Charge of the Electron Measured
Electrons
Missing Target
Electrons Hitting
Target
Crookes Tube
Vacuum Tube
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 Particles having mass
(Electrons)
Carrying the smallest possible unit of
charge
The Plum Pudding Model
J.J. Thompson- 1904
Electrons
(Negativly Charged)
Field
(Positively Charged)
In Today's Vernacular- The Chocolate Chip Model
Discovery of the Nucleus
Earnest Rutherford-1911
Rutherford called it a“Central Charge
(1920 called it a Proton)
Bohr,s Model
1913 – Atomic Model with Fixed Orbits proposed –
Modeled after the Solar System
The Atom has No
Charge
Protons
Number of Protons =
Number of Electrons
Electrons
Inner Orbit
Nucleus
Outer Orbit
Nucleus
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)----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 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
Sometimes the nucleus of an element weighed differently
than another nucleus of the same element
Rutherford – 1920 Postulated a Neutron Doublet
Irene and Fredrick Joliot- Curie 1932 found
radiation they thought was protons
James Chadwick Didn’t Believe It
Discovery of the Neutron
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
Bohr Model of Hydrogen and Helium
Bohr Model of
Potassium(K) and Uranium (U)
39P
19
235U
92
238U
92
92 Protons
92 Protons
20 Neutrons
143 Neutrons
146 Neutrons
Atomic Mass=39
Atomic Mass = 235
Atomic Mass=238
19 Protons
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 GassesHeavier 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???
Mendeleev 1869
Are there
Common
Characteristics
???
H=1
Li=7
Be=9,4
B=11
C=12
N=14
O=16
F=19
Na=23
Mg=24
Al=27,4
Si=28
P=31
S=32
Cl=35,5
K=39
Ca=40
?=45
?Er=56
?Yt=60
?In=75,6
Ti=50
V=51
Cr=52
Mn=55
Fe=56
Ni=Co=59
Cu=63,4
Zn=65,2
?=68
?=70
As=75
Se=79,4
Br=80
Rb=85,4
Sr=87,6
Ce=92
La=94
Di=95
Th=118?
Zr=90
Nb=94
Mo=96
Rh=104,4
Ru=104,4
Pd=106,6
Ag=108
Cd=112
Ur=116
Sn=118
Sb=122
Te=128?
J=127
Cs=133
Ba=137
Original Table – 63 Elements
?=180
Ta=182
W=186
Pt=197,4
Ir=198
Os=199
Hg=200
Au=197?
Bi=210?
Tl=204
Pb=207
Periodic Table
Of The Elements
Alkali Metals
Alkaline Earth
Noble Gasses
Families
Trans
Uranic
The End
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