Timeline of the development of Atomic Struture

Events

(442 BCE) Democritus suggested that atoms were the smallest piece of matter

442

(1800) John Dalton made several statements about atoms such as that all matter is made of atoms

1800

(1897) J.J Thompson discovered electrons and proved atoms were not the smallest objects

1897

(1903) Hantaro Nagaoka made a model of the atom similar to Saturn and its rings

1903

(1911) Ernest Rutherford proved that an atom must contain a center (known as the nucleus)

1911

(1914) H.G Moseley established atomic number of an element is equal to the number of protons in the nucleus

1914

(1922) Niels Bohr stated that electrons occupy particular orbits or shells around the nucleus of an atom.

1922

(1932) James Chadwick discovered neutrons by bombarding atoms with alpha particles

1932

(1940) Glen Seaborg found several radioactive elements and developed the actinide transition series

1940