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450
Democritus's Atomic Theory
-Democritus
-450 BC
-First atomic theory- Atoms are the smallest particles of matter that cannot be split anymore.
-He came up with the first atomic model
-Atoms were small, hard, particles that were all made up of the same materials, but with different sizes and shapes.
-He is the one who came up with the whole topic of atoms in the first place. -
Dalton's Atomic Theory
John Dalton
1803
His Atomic Theory:
-Elements made of atoms
-Atoms of different and same size, mass, and other properties
-Cannot be created, destroyed, or subdivided
-Combined atoms= Compounds
-Chemical Reactions: Atoms separated, combined, or rearranged.
He thought that an atom was a round ball, rather than made up of different shapes and sizes.
He thought that an atom was a round ball (much like a billiard ball)
His work later influenced the works of JJ Thomson -
Thomson's Atomic Model
JJ Thomson
1897
Discovered the electron
He added a negative charge to Dalton's model
Plum Pudding model: Dalton's model with added electrons
He was influenced by Dalton's atomic theory and Aristotle's scientific method. -
Quantum Theory
Max Planck
1900
Creates Quantum Theory
Worked off of energy found by previous scientists
Did not edit atomic model -
Oil Drop Experiment
Robert Millikan
1908
Discovered the charge of an electron independently
Went off of Thomson's discovery of the electron, then found the charge of said electron.
Did not change the atomic model
Went off of Thomson's electron discovery. -
The Atomic Number
Henry Moseley
1911
Creates the idea of the Atomic Number
This is able to establish the number of protons and neutrons within an atom
Does not change the model
Works off of balancing atomic charges discovered by other scientists. -
Rutherford's Atomic Theory
Ernest Rutherford
1909/1911
Discovered the nucleus and determined the atom's empty space
He disproved Thomson's "Plum Pudding Model" of the atom
The atom has a nucleus with electrons orbitting around it. The rest is empty space.
His model was later refined by Niels Bohr and James Chadwick -
Bohr's Theory
Niels Bohr
1913
Refined Rutherfords model.
-Electrons travel without losing energy
-Higer energy electrons travel further away from nucleus and lower energy electrons travel closer to nucleus
-Only move in fixed orbits
Enhanced Rutherfords model of the atom
James Chadwick later works off of Bohr's research -
First Table of Elements
Antione Laviosier
18th Century
Created the basic table of elements
This led to what we know as the Periodic table today
Did not change atomic model
WIthout his table, all of the other discoveries would not have been possible. -
The Uncertainty Principle
Werner Heisenberg
1924
Created The Uncertainty Principle:
-To view an electron in its orbit, you must shine a wavelength of light on it that is smaller than the electron's wavelength.
-This small wavelength of light has a high energy.
-The electron will absorb that energy.
-The absorbed energy will change the electron's position.
Added to Bohr's theory and model of the atom
Worked off of Bohr's model -
Equations of the Electron
Erwin Schrodinger
1926
Came up with a series of equations or wave functions for electrons.
Used The Uncertainty Principle to help create his equations.
Worked off of Heisenberg's Uncertainty Principle -
Chadwick's discovery
James Chadwick
1932
Discovers the neutron (particle with no charge)
Enhanced Bohr's model
Refined Bohr's model and proved the validity of the neutron that Rutherford proposed
