Chemistry II
Atomic Theory History
Tutorial
Time Periods
• 500 BC – 1600 AD: The Alchemical
Era
• 1600 AD – 1800 AD: The Transitional
Time Period
• 1800 AD – 1900 AD: Dalton’s Atom
• 1900 AD – Present: The Quantum
Era
Alchemical Era: 500 BC – 1600 AD
• Democritus ~ 450 BC: He is the originator
of the term, “Atomos”, meaning indivisible.
• Empedocles ~ 400 BC: He is the originator
of the Four Element Theory, Earth, Air,
Fire, and Water.
• Aristotle ~ 350 BC: He added to the Four
Element Theory that matter has the
properties of hot, cold, dry, and wet.
Transitional Time Period:
1600 - 1800
• Robert Boyle – 1661: He publishes the book The
Skeptical Chemist, which disproves the four
element theory.
• Antoine Lavoisier – 1770’s: His greatest
contributions were the co-discovery of oxygen,
gunpowder manufacture, and law of
conservation of mass.
• Sir Isaac Newton – 1642 – 1727: He freed
science from “Godlessness” as it was thought of
by the church.
Other Key Transitional Scientists
• Galileo Galilei – 1564 - 1642
• Charles Augustin de Coulomb – 1736 –
1806
• Phlogiston Theory: The theory that fire is
caused by the release of a substance
called “phlogiston”
• Joseph Priestly – 1733 - 1804
1800 AD – 1900 AD: Dalton’s
Atom
• John Dalton – 1803: Dalton’s atomic
theory reverts back to Democritus
– Matter is composed of small, indivisible
particles called atoms
– The atoms of a given element are identical
– The law of definite composition
– Compounds are created by atoms bonding
through chemical reactions
More Dalton era chemists
• Amadeo Avogadro – 1809: He worked
with gases and confirmed Dalton’s theory.
• Dmitri Mendeleev – 1866: He arranged the
elements into groups in the first periodic
table.
• Joseph Louis Gay-Lussac – 1802: He also
worked with gases and has a funny name.
1900 AD – Present: The
Quantum Era
• The discovery of Sub-atomic particles
– Cathode Rays – the electron was the first
sub-atomic particle discovered by Crookes
and Thomson
– Rutherford’s Gold Foil Experiment: He
learned that atoms contain a dense, positively
charged nucleus, due to protons in nucleus
– James Chadwick discovers the neutron
• Neils Bohr – Modifies the atomic model
once again.
Radioactivity
• X-Rays were first discovered by Wilhelm
Roentgen (Nobel site)
• Henri Becquerel accidentally discovered
radiation
• Marie Curie discovered various radioactive
elements
• Ernest Rutherford defines radiation as
Alpha (a), Beta (b), and Gamma (g) rays
Manhattan Project
• Began in the 1940’s as a race to produce the
first atomic weapon to end WWII
• Directed by American, J. Robert Oppenheimer,
who studied under Thomson
• Enrico Fermi constructed the first nuclear pile
(for a controlled nuclear reaction)
• Albert Einstein started Roosevelt on the project
• Three labs: Hanford, Los Alamos, and Oak
Ridge
Quantum Chemistry
• Max Plank wins the Nobel Prize in 1918
for his theory of the wave-particle duality.
• In 1925, Erwin Schrodinger proposed an
equation to describe the shapes of orbitals
in an atom.
• Werner Heisenberg supports Schrodinger
with is Uncertainty Principle.
• Quantum theory now begins to meld into
the area of physics
What’s Next
• First you must master the history of the
atom
• Then we will learn about the work of
Mendeleev and Seaborg on the periodic
table
• After that, we will begin to put atoms
together to form molecules
• Enjoy