Atomic Time Line

Question 1

Democritus

Answer 1

460 b.c
“by convention bitter, by convention sweet, but in reality atoms and void”
Argued that all matter is composed of atoms which could differ in shape and size

Question 2

James Chadwick

Answer 2

Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron.

Question 3

John Dalton

Answer 3

Proposed an “atomic theory” with spherical solid atoms based upon measurable properties of mass.

Question 4

Eugen Goldstein

Answer 4

Used a CRT to study “canal rays” which had electrical and magnetic properties opposite of an electron.

Question 5

Robert Millikan

Answer 5

Oil drop experiment determined the charge and the mass of an electron.

Question 6

Ernest Rutherford

Answer 6

Using alpha 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. He also assumed that the electrons were located outside the nucleus.

Question 7

Erwin Schrodinger

Answer 7

Viewed electrons as continuous clouds and introduced “wave mechanics” as a mathematical model of the atom.

Question 8

J.J. Thompson

Answer 8

• Pudding model
• Discovered electrons
• Used a CRT to experimentally determine the charge to mass ratio of an electron
• Studied “canal rays” and found they were associated with the proton H +

Question 9

Niels Bohr

Answer 9

Orbital electrons around a nucleus
Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of successive orbital shells of electrons.