Proponents of Atom theory Flashcards
First proposed the concept of “four elements” (fire, air, water, and earth) as the basic composition of matter.
Empedocles (490-435 BC)
Greek philosopher who supported the idea of Empedocles and added the fifth element which he called quintessence.
Aristotle (384-323 BC)
Greek philosopher who assumed the presence of a void in which the unchanging particles were in continuous random motion. Authored the theory stating that everything is composed of small indivisible particles which he called atomos.
Democritus (460-370 BC)
An English chemist who proposed that Atoms have fixed weights and definited properties. Postulated an atomic theory.
John Dalton (1803)
An English chemist who developed an electrically discharged tube with a vaccuum.
Sir William Crookes (1832-1919)
An English physicist who discovered the electron, the first subatomic particle to be discovered. Created the plum-pudding model to demonstrate that atoms are made up of these negatively-charged particles.
Sir Joseph John Thomson (J.J. Thomson)
American physicist, determined the charge of an electron. Electrons are identical and they are components of all types of matter.
Robert Millikan
New Zealand physicist. In a gold foil he measured the deflection of alpha particles aimed at the metal film and observed that most of the particles were not deflected.
Also discovered the nucleus, a concentrated mass in the middle of the atom which surrounded by electrins with enough negative charges to make the atom electrically neutral.
Ernest Rutherford
Danish physicist, suggested that the total energy of an electron is quantized, i.e., restricted to having only certain specific values. The only way an electron can change its energy is to move from one discrete energy level to another. This is the reason why atoms do not collapse. Also, this become the basis for the modern atomic theory, which states that matter is composed of small particles called atoms, which has quantum properties.
Niels Bohr
