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Atomic Models
Democritus to Rutherford
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Democritus (460—370 BC)
• Greek Philosopher
• Atomism
• Nothing exists but atoms
and empty space;
everything else is opinion.
• Atom comes from atomos
meaning uncuttable.
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1 Democritus Atomic Theory
1.
All matter consists of INVISIBLE
PARTICLES…..called atoms
2.
Atoms are
3.
4.
5.
6.
• Solids are made of small, pointy atoms.
• Liquids are made of large, round atoms.
INDESTRUCTIBLE & UNCHANGEABLE
A VOID (empty space) exists between atoms
Atoms are SOLID
Atoms are HOMOGENEOUS……(no internal structure)
Atoms DIFFER in size, shape, mass, position,
• Oils are made of very fine, small atoms
that can easily slip past each other.
• Sweet things are made of smooth atoms,
bitter things of sharp atoms
arrangement…..
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John Dalton (1766--1844)
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Dalton‛s Atomic Model
1.
• A New System of
All matter consists of
TINY PARTICLES
Chemical Philosophy
• Developed the 1st useful
2. Atoms are
INDESTRUCTIBLE &
UNCHANGEABLE
Atomic Theory
• Good at experiments
• 1st to associate atoms
with stoichiometry
3. Elements are characterized by
ATOMIC MASS
4. When elements react, their atoms
combine in WHOLE NUMBER RATIOS
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2 Dalton‛s Laws
J. J. Thomson ( 1856--1940)
• Law of Constant Composition
(aka Law of Definite Proportions)
Discovered electrons
in 1891
for a given compound, the composition is always the same:
H2O
CO2
Cathode ray tubes
CH4
Plum Pudding Atomic
Model
• Law of Multiple Proportions
different compounds may be formed from the same
elements in different, but fixed, ratios:
H2O & H2O2
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CO2 & CO
CH4 & C2H6
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A Cathode Ray Tube
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(1871--1937)
Discovered the nucleus
in 1911
Gold Foil Experiment
Planetary Atomic Model
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4 Rutherford‛s explanation for
both
large- and small-angle scattering,
was the
nucleus
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Empty space!!
If an atom were the
size of a baseball
stadium,
The nucleus would
be the size of a
PEA
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5 Structure of the Nucleus
A Model of Helium
2 protons
2 neutrons
2 electrons
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Elements Chart
Element
Symbol
Atomic
#
Atomic
Mass
Mass
#
#
Protons
# Electrons
# Neutrons
H
1
1.008
1
1
1
0
He
2
4.003
4
2
2
2
O
8
N
7
C
6
F
9
P
15
Sn
50
C-14
6
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6 Isotopes
Same Atomic Number, Different Atomic Mass
Same # of Protons, Different # of Neutrons
1 proton, 0 neutrons
Hydrogen
Deuterium
Tritium
(heavy hydrogen)
(heavier hydrogen)
1 proton, 1 neutron
1 proton, 2 neutrons
Carbon-12
6 protons, 6 neutrons
Carbon-13
6 protons, 6 neutrons
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Alkali Metals
Boron Family
Alkaline Earth Metals
Transition Metals
Carbon Family
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Nitrogen Family
Oxygen Family
Halogens
Noble Gases
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Source of Images and Text gas liquid http://antoine.frostburg.edu/chem/senese/101/atoms/dalton.shtml http://dbhs.wvusd.k12.ca.us/Rutherford-Model.html
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