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2.02 Atomic Parts
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What is an atom?
What are the parts of an atom?
How are these part put together?
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The parts:
Electrons - Thomson (1904), Millikan (1909)
Protons - Goldstein (1886) Rutherford (1911)
Neutrons - Sir James Chadwick (1932)
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Faraday
Electrolysis
~1832
Balmer
Discharge Tubes
~ 1830 - 90
Thomson
e/m
~1897
Millikan
e
~1909
Mendeleev
Periodic Table
~1870
Michelson
C
~1885
Becquerel, Curie
Radioactivity a,b g
~1897
Planck
Quantum
~1900
Rutherford
Nucleus
~1911
Einstein
E=hv, E=mc
~1905
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Bohr
Shell Model
~1913
Aston
Isotopes
~1909
Stern, Gerlach
Electron Spin
~1921
Schrodinger
Wave Model,
Pauli Exclusion,
Hund's Rules
~1926
deBroglie
Matter Waves
~1924
Heisenberg
Uncertainty Principle
~1927
Chadwick
Neutron
~1932
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Matter contains negative charge particles;
electrons. Later cathode rays were discovered
and into the late 1800's question of cathode
rays identity were put forth.
An electroscope demonstrates
electric charge. (a) With no
electrical influence, the foil leaf
hangs straight down. (b) A rubber
rod that had been rubbed with fur
was touched to the bulb of the
electroscope. (The rod was
withdrawn slightly before this
photograph was made.) The electric
charge that had built up on the rod
flowed onto the electroscope, and
the movable leaf diverged from the
stationary leaf. The reason for this
observation is that the same charge
has flowed onto both leaves. Because
like charges repel, the leaves repel
each other. (C. D. Winters)
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2.02 Atomic Parts
Cathode rays were electrically
charge particles.
• Cathode Ray tube with electron
stream where deflected by
positive and negative plate.
• e/m = -1.76•108 C/g
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Proposed the "plum pudding
model" theory of the atom;
Coulomb's Law:
F = k Q1 Q2 / r2.
Atoms contains protons and
electrons.
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Oil drop experiment to determine the
charge value of the electron
e = -1.60•10-19 V
m = 9.11 •10-31 kg
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Gold thin foil experiment with alpha radiation through gold foil
proved that the atom consisted with a very dense nucleus. Based
on the particles deflection pattern, Rutherford calculated the
fraction of the atomic volume occupied by the positive nuclei, that
is 1 part in 1014. The mass is so dense that a nucleus the size of
a pea would have mass greater that 250 million tons. This led to
the modern view of the atom (nucelar atom)
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Scientific Method development of the atomic theory.
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The parts: Subatomic particles and their properties
Particle
Mass
*Rel Mass
Rel Charge
(amu)
e-; electron
p+; proton
n;
10
neutron
-31
9.109•10
-27
1.673•10
-27
1.675•10
Kg
1/1837
Kg
1
Kg
1
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-19
- 1.602•10 C
-19
+ 1.602•10
C
0
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These were the experiments which
leading to the discovery of the parts of
the atom. The picture of the atomic
architecture is now complete. (Or is it?)
Three particles - electron, protons, and
neutrons combine in various numbers to
make the 118 (and counting) elements of
the periodic table.
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