Atomic Structure Timeline (Chemists)

Democritus – 400BC
Proposed that all materials are made by tiny particles called atoms.

Aristotle – 400BC
-Proposed 4 elements (fire, water, wind, earth)
-Thought matter was “continuous” (no such thing as particles)

Isaac Newton – 1660 – English scientist, astronomer, mathematician
-Real Experiments
-Published paper stating their belief of atomic particle
-atoms = tiny spheres

Robert Boyle – 1662 – British scientist
-Real experiments
-published paper stating his belief of atomic particle
-atoms = tiny spheres

Antoine Lavoisier – 1777 – French chemist
-Built first balance = first way to measure changes in mass (in reactions)
-Proposed “law of conservation of mass/matter”

Joseph Proust – 1799 – French chemist
-Proposed “law of definite proportions”
-“Atoms combine in definite, whole number, ratios.”

John Dalton – 1803 – English school teacher
-Poor school teacher in England
-Based on other people’s experiment

Dalton’s Atomic Theory
1.) Matter is composed of small particles called atoms.
2.) All atoms of a given element are identical in mass and properties
3.) Atoms combine in definite whole-number ratios.
4.) A chemical reaction is a REARRANGEMENT of atoms (like law of conservation)

Joseph Gay-Lussac – 1808 – French Chemist and Physicist
2 Gas Laws:
1.) Law of combining volumes
2.)Pressure-temperature law

Wm. Crookes -1870 – English physicist
Pioneer of Vacum Tubes
-Crooks Tube
-Crookes radiometer

Henry Becquerel – 1896 – French – Accidental Discovery
Discoverer of Radioactivity

J.J. Thompson – 1897 – “Plum pudding”
Discovered and identified the electron.

Albert Einstein – 1905 – German-Swiss mathematician
-Theory of relativity
-mass energy equivalence formula (E=mc (squared))
-Wrote Roosevelt to start researching atomic bombs like Hitler
-Denounced nuclear weapons

Robert Millikan – 1909 – American Physicist
-Nobel Prize Winner
-Measured elementary electronic charge

Ernest Rutherford – 1911 -Born in New Zealand – Did work in Cambridge
-Used polonium (positively charged) in container with lead barrier, and a gold foil.
-Discovered nucleus

Henry Moseley – 1913 – British physicist
-Created concept of atomic number
-helped organize periodic table

Neils Bohr – 1913 – Danish physicist
-Contributed to atomic structure and quantum mechanics.