Democritus c. 460Abdera, Thrace, Greece
Formulated an atomic theory for the cosmos. His speculation on atoms gave an understanding of atomic structure. Many consider him as the ‘father of modern science.’
Newtown 1704Lincolnshire, England
Proposed a mechanical universe with small solid masses in motion. He also suggested that atoms were held together by attractions that we now call forces. His work has enabled other scientists such as Dalton to develop the atomic theory.
Dalton 1803Cumberland, England
Proposed an ‘atomic theory’ with spherical solid atoms based upon measurable properties of mass. His idea was later extended. He also printed the first published table of relative atomic weights.
Proposed that electricity was made of discrete negative particles he called electrons. He has introduced the term electron as the ‘fundamental unit quantity of electricity’ and now it is widely used.
J.J. ThomsonManchester, England
Used a CRT to experimentally determine the charge to mass ratio of an electron. He has been credited for the discovery of the electron and of isotopes.
Used the idea of quanta (discrete units of energy) to explain hot glowing matter. He was the founder of the quantum theory and is one of the most important physicist of the twentieth century.
Postulated a ‘Saturnian’ model of the atom with flat rings of electrons revolving around a positively charged particle. He was a pioneer of Japanese physics. He work was later extended and pursued by Rutherford.
Millikan 1909Illinois, USA
Worked on an oil drop experiment that determined the charge and the mass of an electron. His experiment was accurate and was used by other scientists.
E. Rutherford 1911Brightwater, New Zealand
Published his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons . This helped develop the atomic theory as we know it today. He was known as the ‘father of nuclear physics.’
H.G.J. Moseley 1914England
Used x-ray tubes to determine the charges on the nuclei of most atoms. He showed that atomic numbers had a strong physical basis.
Bohr 1922Copenhagen, Denmark
Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His work made foundational contributions to understanding atomic structure and quantum mechanics.
James Chadwick 1932Cheshire, England
Used alpha particles to discover a neutral atomic particle with a mass close to the proton. Thus was discovered the neutron. He discovered the neutron which allowed for further development to occur into atomic structure.