Democritus - an influential Ancient Greek pre‑Socratic philosopher. He is remembered today for his formulation of an atomic theory of the universe.
JJ Tomson - In 1897 Thomson showed that cathode rays were composed of a previously unknown negatively charged particle. Thomson was awarded the 1906 Nobel Prize in Physics for the discovery of the electron.
John Dalton - An English chemist, meteorologist and physicist. He is best known for his pioneering work in the development of modern atomic theory.
Gold Foil Experiment - a landmark series of experiments by which scientists discovered that every atom contains a nucleus where its positive charge and most of its mass is concentrated.
Cathode Ray Tube- a vacuum tube containing one or more electron guns, and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beams onto the screen to create the images.
Antoine Lavoisier - a French nobleman and chemist central to the 18th-century Chemical Revolution and a large influence on both the histories of chemistry and biology.
Plum Pudding Atomic Model - a model of the atom that incorporated the recently discovered electron, and was proposed by J. J. Thomson in 1904.
Bohr Planetary Model - where the negatively charged electron confined to an atomic shell encircles a small, positively charged atomic nucleus and where an electron jump between orbits is accompanied by an emitted or absorbed amount of electromagnetic energy.
Robert Millikan - American experimental physicist honored with the Nobel Prize for Physics in 1923 for his measurement of the elementary electronic charge and for his work on the photoelectric effect.
James Chadwick - English physicist who was awarded the 1935 Nobel Prize in physics for his discovery of the neutron in 1932.
Erwin Schrödinger - Nobel Prize-winning Austrian physicist who developed a number of fundamental results in the field of quantum theory, which formed the basis of wave mechanics.
Niels Bohr - Danish physicist who made foundational contributions to understanding atomic structure and quantum theory, for which he received the Nobel Prize in Physics in 1922.
Law of Conservation of Mass - states that for any system closed to all transfers of matter and energy (both of which have mass), the mass of the system must remain constant over time, as system mass cannot change quantity if it is not added or removed.
Dalton's Atomic Theory - presented an important series of papers, entitled "Experimental Essays" on the constitution of mixed gases; on the pressure of steam and other vapours at different temperatures, both in a vacuum and in air; on evaporation; and on the thermal expansion of gases.
Ernest Rutherford Model -Rutherford's new model for the atom, based on the experimental results, contained the new features of a relatively high central charge concentrated into a very small volume in comparison to the rest of the atom and with this central volume also containing the bulk of the atomic mass of the atom.
Quantum Mechanical Model - fundamental branch of physics which deals with physical phenomena at nanoscopic scales where the action is on the order of the Planck constant.
Electron Cloud Model - mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus.
Ernest Rutherford - he discovered the concept of radioactive half-life, proved that radioactivity involved the transmutation of one chemical element to another, and also differentiated and named alpha and beta radiation.
Dmitri Mendeleev - He formulated the Periodic Law, created his own version of the periodic table of elements, and used it to correct the properties of some already discovered elements and also to predict the properties of eight elements yet to be discovered.
Henry Moseley - was an English physicist. Moseley's outstanding contribution to the science of physics was the justification from physical laws of the previous empirical and chemical concept of the atomic number.