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 (), Beta (), and Gamma () 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