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Democritus
Ancient Greek philosopher living from 460 BC to 370 BC. He claimed everything is made of atoms. Atoms have empty space between then, are indestructible and always in motion. There are infinite numbers and kinds of atoms, different in size and shape. -
Antoine Lavoisier
Named the oxygen element in 1778 and hydrogen in 1783. He also discovered the role oxygen plays in combustion. -
John Dalton (Dalton's Atomic Theory)
Discovered that matter is made of atoms which are indivisible and indestructible. All atoms of a given element are identical in properties and mass. The rearrangement of atoms is a chemical reaction. Atoms can’t be created or destroyed. A combination of two or more different kinds of atoms is compounds. -
Dmitri Mendeleev
In the late 1860s, he organized the known elements and was looking for patterns in properties. He found the pattern to place elements in order of increasing atomic mass. This is how the periodic table was created. -
J. J. Thomson (Plum Pudding Atomic Model)
In 1897, he discovered the electron. Also discovered that an atom consists of a sphere of positive charge with negatively charged electrons on it. The negative and positive charges in an atom are equal in magnitude, meaning an atom is electrically neutral. -
Robert Millikan
Measured the charge on an electron with an oil-drop experiment and was able to discover the mass and charge of the electron. -
Ernest Rutherford (Rutherford Model) - Gold FOil Experiment
In 1909, Rutherford conducted an experiment and discovered that some of the alpha particles bounced back instead of most of them going through the gold foil. -
Niels Bohr
He refined Rutherford’s model in 1931, proposed that electrons orbit the nucleus without losing energy and could only move in fixed orbits of specific energies. Also, that low energy-electrons would orbit closer to the nucleus while high energy-electrons would orbit further from the nucleus. -
Erwin Schrodinger
In 1926, he used mathematical equations to finding an electron in a certain position. -
Henry Moseley
Developed the application of X-ray spectra to study atomic structure. Discovered accurate positioning of the elements in the Periodic Table. -
James Chadwick
In 1932, he proved the existence of neutrons. He established that the atomic number is determined by the numbers of protons that are in an atom. -
Quantum Mechanical Model
The Quantum theory confirms that matter has properties that are associated with waves, and so the model uses mathematics and is based on this theory. -
Bohr Planetary Model
Used as a symbol for atomic energy. The neutrons and protons use a dense and central area which is the nucleus. The electrons orbit the nucleus. -
Electron Cloud
Developed by Erwin Schrodinger and Werner Heisenberg. The electron cloud shows where the electrons are when they rotate around the nucleus of an atom. This model also states that electrons do not orbit the nucleus. -
Cathode Ray Tube
Invented by Ferdinand Braun in 1897 but was made famous by J.J. Thomson. The electrons are accelerated into a tube, onto a screen that creates pictures and images.
