-
500
Democritus
Democritus, greek philospher, discovers -
John Dalton
he proposed "atomic theory" with spherical solid atoms based on physical properites of mass, -
Dimitri Mendeleev
Arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights". This became known as the Periodic Law -
Sir William Crookes
Discovered cathode rays had the following properties: travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass. -
JJ Thomson
Studied "canal rays" and found they were associated with the proton H+ he also used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 108 -
Rutherford
Studied radiations emitted from uranium and thorium and named them alpha and beta.He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus. -
Neils Bohr
Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of sucessive orbital shells of electrons.