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470
Democritus - Greece
-extended his mentor, Leucippus’ atomic theory
-formulated an atomic theory for the cosmos
-the ideas that both his mentor and him are remarkably similar to modern-day science.
-suggested that all matter is made of tiny particles which differ from each other in form, position, and arrangement -
Isaac Newtown - England
-Theory of light
-Suggested the planets orbiting path.
-Three laws of motion -Proposed that atoms were held together by an attraction called force. Also suggesting that atoms were made up of small round spheres. -
John Dalton - England
-all matter was made up of small particles called atoms.
-each of the elements atoms are unique in size and weight.
- Three types of atoms exist: simple (elements), compound (simple molecules), and complex (complex molecules). -Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass.
-found the approx. weight of atoms.
-all elements are made of atoms. -
George Johnstone Stoney - Ireland
-the Stoney scale
-proposed the term electron
-conception and calculation of an atom’s electric charge -Proposed that electricity was made of discrete negative particles he called electrons; introduced the idea of negative charge -
Joseph John Thomson - England
-discovery of the electron and of isotopes
-prove atoms had subatomic atoms
-Plum Pudding model - allowed us to know about the existence of subatomic particles through cathode rays -
Max Planck - Germany
-quantum theory
-created Planck’s constant
-created Planck’s Law of Black-body Radiation The quantum theory was to be the foundation of our understanding of atomic and subatomic processes -
Hantora Nagaoka - Japan
-Saturnian Model
-Spectroscopy -even though the model created was incorrect it was based on the planetary positions and was a bases to the modern day model. -
Robert Andrews Milikan - America
-measurement of the charge on the electron using the oil drop experiment
-photoelectric effect -allowed us to measure the charge to mass ratio of an electron -
Ernest Rutherford - New Zealand
-discovered the concept of radioactive half life
- proved that radioactivity involved the transmutation of one chemical element to another
- differentiated and named alpha and beta radiation
-created the Rutherford model of the atom which is which is a small positive charged and orbited by electrons
-claimed that the nucleus was dense and positively charged.
-claimed electrons were outside the nucleus -
Henry Gwyn-Jeffreys Moseley - England
-justification from physical laws of the previous empirical and chemical concept of the atomic number
-arranged the periodic table by their atomic numbers
-Moseley Law that is an empirical law concerning the characteristic x-rays that are emitted by atoms -After using Xray tubes to examine the atoms, he determined that the stomic number of an element is equal to the number of protons in the nucleus.
-reorganised the perodic table so it was to be in the o -
Niels Bohr - Denmark
-understanding of the structure of properties of atoms
-the Bohr model of the atom’s shell which had atoms built up of successive orbital shells of electrons
-the correspondence principle
-the liquid drop model of the atomic nucleus -developed an explanation of atomic structure that underlies regularities of the periodic table of elements.
- suggested that the outer orbits could hold more electrons than the inner ones, and that these outer orbits determine the atom's ch -
James Chadwick - England
-discovery of the neutron
-Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron.
