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Democritus
Democritus was the first to suggest the existence of the atom -
John Dalton
Suggested that the atom was an indivisible particle. -
Antoine Lavoisier
He created the Law of Conservation of Mass. -
Law of Conservation of Mass
States that in a chemical reaction, the mass of the product equals the mass of the reactants. Developed by Antoine Lavoisier. -
Dalton's Atomic Theory
Said that all matter is made up of atoms. Atoms are indivisible and indestructible. All atoms of a given element are identical in mass and properties. Compounds are formed by a combination of two or more different kinds of atoms. A chemical reaction is a rearrangment of atoms. -
Dmitri Mendeleev
He formulated the Table of Elements- listing them by their atomic weight and grouping them into "families" with similar characteristics. -
JJ Thomson
Thomson showed that electrons have negative electric charge and come from ordinary matter. -
Cathode Ray Tube
Thomson found that the mysterious glowing stream would bend toward a positively charged plate. He theorized, and was later proven correct, that the stream was in fact made up of small particles, pieces of atoms that carried a negative charge. These particles were later named electrons. -
Quantum Mechanical Model
An atomic model in which electrons are treated as waves; also called the wave mechanical model of the atom. -
Plum Pudding Atomic Model
Proposed that the negatively charged electrons (the plums) were mixed with smear-out positive charges (the pudding.) This model explained the neutrality of bulk material, yet still allowed the description of the flow of electric charges. -
Robert Millikan
He did an experiment which measured the charge of the electron. -
Rutherford Model
He shot alpha particles into a foil of gold. -
Gold Foil Experiment
Rutherford fired tiny alpha particles at solid objects such as gold foil. He found that while most of the alpha particles passed right through the gold foil, a small number of alpha particles passed through at an angle and some bounced straight back. This experiment suggested that golf foil, and matter in general had holes in it. -
Ernest Rutherford
Ernest and his co-workers conducted an experiment intended to determine the angles through which a beam of alpha particles (helium nuclei) would scatter after passing through a thin foil of gold. The results were astounding. The vast majority of alpha particles behaved as expected and hardly scattered. But there were alpha particles that scattered through angles greater than 90 degrees. It was evident from this type of experiment that led to the model of the atom as having a nucleus. -
Henry Moseley
By measuring the wavelengths of the x-rays given off by certain metal, Moseley was able to determine the number of positives charges in the nucleus of an atom. This was the first concept of the atomic number. -
Bohr Planetary Model
Showed there are particular orbits in which the electrons do not lose energy and therefore do not spiral into the nucleus. -
Niels Bohr
Created a new model in which there are particular orbits in which the electrons do not lose energy and therefore do not spiral into the nucleus. This model was the beginning of quantum machanics, which successfully explains many properties of atoms. -
Erwin Schrodinger
Found where the electron is in an atom. -
Electron Cloud Model
An atom model where electrons no longer depicted as particles moving around the nucleus in a fixed orbit. -
James Chadwick
Discovered a third type of subatomic particle which he named the neutron.
