John daltonAll matter is composed of atoms
Atoms cannot be made or destroyed
All atoms of the same element are identical
Different elements have different types of atoms
Chemical reactions occur when atoms are rearranged
Compounds are formed from atoms of the constituent elements.
Sir Joseph John ThomsonSir Joseph John THomson discovered the electron in a series of experiments design to study the nature of electric discharged in ahigh vacume cathode ray tube, an area being investigated by numerous scientist at the time
Philip LenardIn 1902 Lenard showed that an electron must have a certain minimum energy before it could produce ionisation when it passed through a gas.
In 1903 he published his conception of the atom as an assemblage of what he called "dynamides", which were very small and were separated by wide spaces; they had mass and were imagined as electric dipoles connected by two equal charges of contrary sign and their number was equal to the atomic mass
Sir Joseph John ThomsonThomson suggested a model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces.
Ernest RutherfordErnest Rutherford publishes his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons.
Niels BohrThe timing was very fortuitious since shortly before Bohr and Rutherford met, Rutherford had published a major work showing that the bulk of the mass of an atom resided in the nucleus.
James ChadwickChadwick proofs the existence of the neutron in 1932 what accelerated the research in nuclear physics inmensely.