History of Atomic Structure

Timeline created by lisahluu in Science and Technology

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Event Date:	Event Title:	Event Description:
01/01/460	Democritus c. 460	Abdera, 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.’
01/01/1704	Newtown 1704	Lincolnshire, 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.
01/01/1803	Dalton 1803	Cumberland, 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.
01/01/1894	G.J. Stoney	Ireland/England 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.
01/01/1897	J.J. Thomson	Manchester, 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.
01/01/1900	Planck 1900	Germany 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.
01/01/1903	Nagaoka 1903	Japan 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.
01/01/1909	Millikan 1909	Illinois, 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.
01/01/1911	E. Rutherford 1911	Brightwater, 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.’
01/01/1914	H.G.J. Moseley 1914	England Used x-ray tubes to determine the charges on the nuclei of most atoms. He showed that atomic numbers had a strong physical basis.
01/01/1922	Bohr 1922	Copenhagen, 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.
01/01/1932	James Chadwick 1932	Cheshire, 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.