Atom History Flashcards
John Dalton
1803
Dalton’s atomic theory:
1.
Dalton’s Atomic Theory
1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Atoms of a given element are different than those of any other element.
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) Atoms are not created nor destroyed in a chemical reaction.
Democritus
300 B.C.
theorized that elements were fire, water, earth, and air
JJ Thomson
1897
discovered the electron using the cathode ray tube to form the plum pudding model
Millikan
1909
determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron in the oil drop experiment
Ernest Rutherford
1911
Using alpha particles (heavy positively charged particles)as atomic bullets, probed the atoms in a piece of thin gold foil . He established that the nucleus was: very dense, very small and positively charged.
Henry Moseley
1914
determined the charges on the nuclei of most atoms and discovered the atomic number (equal to the number of protons in the nucleus)
Niels Bohr
1922
discovered that atoms contain electrons that formed successive orbits
Erwin Schrodinger
1930
- introduced “wave mechanics” as a mathematical model of the atom in a quantum mechanical model
- his equation limits an electron’s energy to certain values and calculates the likelihood of finding an electron in a particular location
James Chadwick
1932
discovered the neutron using alpha particles discovered a neutral atomic particle with a mass close to a proton.