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History of the
Atomic Theory
Ancient Greeks (B.C.)
• Aristotle
• Four Elements:
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Earth
Water
Air
Fire
Greek Atomists
(460B.C.)
• Democritus : Matter was made up of
particles in perpetual motion and
had the following characteristics:
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Invisible
Solid
Indivisible
Eternal
Surrounded by an empty space
Infinite number of Shapes
Greek Atomists
• Archimedes
disagreed with
Democritus
• Archimedes was
very highly
respected and so
everyone believed
what he said
• Democritus’ ideas
were tossed
Alchemy
• During the dark ages, earlier
information was lost.
• During the middle ages, people began to
reinvestigate nature and the structure
of matter
• The plan : TRANSMUTATION
Change plain metals into noble metals
- Lead  Gold
- Alchemists developed the
Observation  Experimentation 
Measurement  Classification
Method.
Boyle (1661)
• Matter was made up of
simple substances called
ELEMENTS
• Elements were substances
that could not be further
decomposed
• He had no PROOF :
qualitative experiments
(what’s in it) no quantitative
experiments (how much)
Lavoisier (1780)
• Developed quantitative
experiments needed to prove
Boyle’s theory
• He heated mercury in air.
• The silver mercury turned to a red
product, which was HEAVIER
200g of Mercury (grey) plus 16g Oxygen yields 216 g of red product
200g Hg + 16g O2  216 g HgO
Lavoisier
• To explain the
increase, he reversed
the experiment and
heated the red product
and collected the gas
released
• Found that the amount
of oxygen produced
was equal to the
increase in mass of his
first reaction
216 g of red product (heated) yields 200g of Mercury plus 16g of Oxygen
216 g HgO  200g Hg + 16g O2
Lavosier
• Demonstrated the Law of
Conservation of Mass;
• Matter is neither created nor destroyed
during a chemical reaction
• Lavoisier classified substances as
elements;
• A substance that cannot be broken down
into simpler substance(s) by chemical
means.
Lavoisier's table of simple substances
Metals
Gases
New names (French)
Old names (English
translation)
Lumière
Light
Heat
Calorique
Oxygène
Azote
Hydrogène
Principle of heat
Igneous fluid
Fire
Matter of fire and of
heat
Dephlogisticated air
Empyreal air
Vital air
Base of vital air
Phlogisticated gas
Mephitis
Base of mephitis
Inflammable air or gas
Base of inflammable
air
New names (French)
Old names (English
translation)
Antimoine
Antimony
Argent
Silver
Arsenic
Arsenic
Bismuth
Bismuth
Cobolt
Cobalt
Cuivre
Copper
Étain
Tin
Fer
Iron
Manganèse
Manganese
Mercure
Mercury
Molybdène
Molybdena
Nickel
Nickel
Or
Gold
Platine
Platina
Plomb
Lead
Tungstène
Tungsten
Zinc
Zinc
Lavoisier's table of simple substances
Earths
Nonmetals
New names (French)
Old names (English
translation)
Soufre
Sulphur
Phosphore
Phosphorus
Carbone
Pure charcoal
Radical muriatique
Unknown
Radical fluorique
Radical boracique
New names (French)
Old names (English
translation)
Chaux
Chalk, calcareous earth
Magnésie
Magnesia, base of Epsom
salt
Baryte
Barote, or heavy earth
Alumine
Clay, earth of alum, base
of alum
Silice
Siliceous earth, vitrifiable
earth
Unknown
Unknown
Dalton (1808)
• Major Contribution: First Atomic
theory based on experimental
evidence.
• Reintroduced the idea of the atom
based on scientific experiments.
• Small particles called atoms
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Can’t be subdivided
Can’t be created or destroyed
Properties of 1 atom are identical
Properties of atoms of different
elements differ
• Atoms combine in simple ways to form
compounds (in definite whole number
ratios)
Thomson (1897)
• Discovered the electron
• Proposed an initial model
(Thomson’s Pudding)
• Sphere of positive
substances mixed with
negative electrons
• AKA Raisin Pudding Model
Millikan (1911)
• Determined the
charge of an
electron
• Used an oil drop
experiment
Rutherford (1912)
• His students were doing
experiments with radiation
• Shot alpha particles through a thin
sheet of gold foil
• Thought that the spaces in the
atoms were mainly empty, BUT
• Some particles were reflected
• Lead to the discovery of the
Nucleus
• The positive charge (or
majority of the atom’s mass)
was concentrated in a small
point.
• Introduced Atomic Planetary
Model
The Rutherford Experiment
Bohr (1914)
• Orbits can’t be anywhere –
they’re quantified
• Quantified – specific numbers
(like quarters)
• Greater the distance from the
nucleus, the greater the
energy of an electron
• Orbits became known as energy
levels
• Every atom in its normal (non
excited) state, the electrons
occupy the lowest energy
levels available.
• Last in what we know as
classical physics
Updating Atomic Theory
• Scientists have learned a great deal
about the structure of matter
• Atoms have many parts and a complex
organization
• The essential ideas of Dalton’s theory
are still useful:
• Elements are made of atoms
• Compounds do form by the joining of atoms
in fixed whole number ratios
• Properties of atoms of 1 element are
identical
• Properties of atoms of different elements
differ.
Updating Atomic Theory
•
3 Major Differences:
1. Atoms can be subdivided
- Made up of protons, neutrons & electrons
2. Atoms can be changed from one element to
another, but only by nuclear reactions
3. Atoms of the same element are not all
exactly alike – they are alike in
characteristics that determine chemical
properties of that element but atoms of the
same element can and DO have different
masses (Isotopes)
Time Line
• BC – Ancient Greeks had the idea of
an atom
• 1808 - Dalton’s atomic theory
• 1886 – Protons discovered
• 1897 – Electrons discovered
• 1911 – Rutherford’s Experiment
• 1913 – Bohr Model of an atom
• 1932 – Neutron discovered
Quantum Physics
• Subatomic Particles
• Electron probability
• Different Shapes
• Charge-Cloud Model
• Doesn’t show paths of
the electrons, instead it
shows the most probable
location of an electron
- Schrödinger
A Review
• Over the last 200 years, (especially in the 1900s)
that many modifications were made to our
conception of the structure of matter.
• Through the creativity and new technologies
utilized by scientists, modifications and
improvements were made.
• Science, technology and the affect of
society’s thinking changed how we think
of nature.
• Atoms are not solid spheres, but a combination of even
smaller parts, each having a unique structure and
function.