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460 BCE
Democritus
Proposed that all matter was made up of small units called, atoms. Democritus never did experience and had little evidence. -
John Dalton
Agreed that all matter was created by atoms. These atoms were believed to be indestructible. Brought forth the idea that all compound pounds are two atoms put together to form a compound. -
Mendeleev
Inventor of the periodic table. How we organize the elements on the periodic table. -
Henri Becquerel
Discovered Radioactivity which then earned him a Nobel Prize
Definition: emission of elementary particles by some atoms when their unstable nuclei disintegrate -
J.J Thomson
Discovered electrons and noticed that atoms can be divided. Concluded atoms are made of positive cores and have negative charged particles. Developed the Plum Pudding Model. -
Cathode Ray Tube Experiment
J. J. Thomson was the one who discovered electrons over the course of three experiments. He used a cathode ray tube (vacuum-sealed tube). -
Gold Foil Experiment
The Gold Foil Experiment proved that there is an existence of a small massive center to atoms which is now known as the nucleus. -
Ernest Rutherford
Discovered the nucleus of an atom has a positive charge. -
Millikan Oil Drop Experiment
Created by: Robert A. Millikan and Harvey Fletcher in 1909 t
Purpose: measure the elementary electric charge
Details: The experiment involved observing tiny charged droplets of oil between two horizontal metal electrodes. -
Fredrick Soddy
Came up with idea of isotopes. Also had part to do with the explanation of radiation being due to transmissions of elements. -
Neils Bohr
Came up with Bohr Experiment. The idea that the outer orbit of an atom holds more electrons that the inner orbits. How we figure out the chemical properties of an atom. -
Bohr Atomic Model
Niels Bohr was the one to introduce this model. This model is a primitive model of the hydrogen atom. What is it? How we figure out the properties of an atom. (Negatively charged electron that is confined into a positively charged atomic nucleus and where an electron jump between orbits is accompanied by an emitted or absorbed amount of electromagnetic energy) -
The Electron Cloud Model
Cloud Model differs from the Bohr Model in that it does not define the exact path of an electron. Instead, it predicts the likely position of the location of the electron based on a function of probabilities. -
Chadwick
Came up with the idea of the neutron. The neutron is responsible for balancing out the proteins in the nucleus of an atom.
