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History of the
Atomic Theory
Ancient Greeks (B.C.)
•Aristotle•Four Elements:
•Earth•Water•Air•Fire
Greek Atomists (460B.C.)
• Democritus : Matter was made up of particles in perpetual motion and had the following characteristics:• 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 : TRANSMUTATIONChange 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.
Gases
New names (French)Old names (English
translation)
Lumière Light
Calorique
Heat Principle of heat Igneous fluid Fire Matter of fire and of heat
Oxygène
Dephlogisticated air Empyreal air Vital air Base of vital air
AzotePhlogisticated gas
MephitisBase of mephitis
HydrogèneInflammable air or gas
Base of inflammable air
Metals
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
Nonmetals
New names (French)Old names (English translation)
Soufre Sulphur
Phosphore Phosphorus
Carbone Pure charcoal
Radical muriatique Unknown
Radical fluorique Unknown
Radical boracique Unknown
Earths
New names (French)Old names (English translation)
Chaux Chalk, calcareous earth
MagnésieMagnesia, base of Epsom salt
Baryte Barote, or heavy earth
AlumineClay, earth of alum, base of alum
SiliceSiliceous earth, vitrifiable earth
Lavoisier's table of simple substances
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
• 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 & electrons2. Atoms can be changed from one element to
another, but only by nuclear reactions3. 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.