-
Period: 460 BCE to 370 BCE
Democritus
"The theory of Democritus held that everything is composed of "atoms," which are physically, but not geometrically, indivisible; that between atoms, there lies empty space; that atoms are indestructible, and have always been and always will be in motion; that there is an infinite number of atoms and of kinds of atoms," -
Period: to
John Dalton
Dalton's atomic theory said that all matter was composed of atoms, indivisible, and indestructible building blocks. <img src="https://www.universetoday.com/wp-content/uploads/2014/12/dalton_atomictheory-e1453320561241.jpg" alt="What Is John Dalton's Atomic Model? - Universe Today"/> -
Period: to
Dmitri Mendeleev
"Mendeleev realized that the physical and chemical properties of elements were related to their atomic mass in a 'periodic' way, and arranged them so that groups of elements with similar properties fell into vertical columns in his table," -
Period: to
Eugene Goldstein
discovered the proton -
Period: to
j.j thomson
j.j thomson experimented with cathode ray tubes and discovered that all atoms contain tiny negatively charged subatomic particles or electrons
<img src="https://www.universetoday.com/wp-content/uploads/2009/08/plum-pudding-model.jpg" alt="What Is The Plum Pudding Atomic Model? - Universe Today"/> -
Period: to
Robert Millikan
"His earliest major success was the accurate determination of the charge carried by an electron, using the elegant “falling-drop method”; he also proved that this quantity was a constant for all electrons (1910), thus demonstrating the atomic structure of electricity," -
Period: to
Ernest Rutherford
Ernest discovered that there are two types of radiation, alpha and beta particles, that come from uranium -
Period: to
Niels Bohr
"proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus but only in prescribed orbits. When jumping from one orbit to another with lower energy, a light quantum is emitted." -
Period: to
James Chadwick
"James Chadwick announced that the core also contained a new uncharged particle, which he called the neutron,"
