-
400
Democritus
-Everything is composed of atoms
-Between atoms lies an empty space
-Atoms are indestructible
-Infinite number of atoms
400 B.C -
Period: 400 to
Atomic Timeline
-
John Dalton
-all matter is made of atoms
-all atoms of a given element are identical in mass and properties
-Compounds are made from combination of 2 or more atoms
-Chemical reaction is an arrangement of atoms
-1803 -
J.J. Thomson
-Discovered the electron
-model of the atom as a sphere in which electrons are positioned by electrostatic forces
-nature of positively charged particles
-1897 -
Robert Milliken
-Measured the charge of an electron
-Millikens oil drop apparatus
-1908 -
Ernest Rutherford
-Postulated the nuclear structure of an atom
-Discovered positively charged central region of the atom
-1911 -
Neils Bohr
-Explained what happened inside an atom and and developed a picture of atomic structure
-first to discover that electrons travel in separate orbits around the nucleus and the number of electrons in the outer orbit determines the property of an element
-number 107 on the periodic table is named after him
-1913 -
James Chadwick
-Discovered the neutron
-Believed neutron to be a complex particle consisting of a proton and an electron
-1932
