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460
Democritus (Greece)
Continued and expanded on his master Leucippus’ ideas. Democritus was right in believing that everything was composed of matter
Contribution: All things are composed of atoms with a void (where atoms move) between them. -
Newton (England)
Mechanical universe with small solid masses in moveme
Contribution: Atoms are held together by attractions. -
Dalton (England)
Mechanical universe with small solid masses in movement
An ‘atomic theory’ with spherical solid atoms which were based on properties of mass.
Contribution: 1)all matter consists of tiny particles. 2)atoms are indestructable and unchangeable.
3) elements are classified by the mass of their atoms. 4)when elements react, their atoms combine in simple whole number ratios. -
G.J. Stoney (Ireland)
Electricity is composed of negative particles know as electrons.
Contribution: Contributed to the understanding of electricity of an atom. This laid foundations for J.J Thomson, who eventually discovered the electron. -
J.J. Thomson (England)
Determined the charge of an electron as 1.759 x 108.
Contribution: Identified that electrons in an atom could show- i.e. atoms were not invisible. He suggested an atom model of a sphere of positively charged matter surrounded by negatively charged electrons. -
Planck (Germany)
Explained hot glowing matter based on the idea of quanta (discrete units of energy) .
Contribution: Planck was considered to be the father of Quantum. -
Nagaoka
Model of atom like Saturn, named Saturnian. Electrons with flat rings revolving a positively charged particle.
Contribution: Created an incorrect and unstable electron movement ‘atomic theory’ based on the rings of Saturn. -
Millikan (America)
An experiment involving an oil drop determined the charge and mass of an electron.
Contribution: Using the ‘falling-drop method’, Millikan correctly determined the negative charge of an electron, proving that this charge was constant with all electrons. He demonstrated the atomic structure of electricity. -
Rutherford (New Zealand/ NZ)
Discovered that the nucleus of an atom is very dense, small and positively charged. Assumes that electrons are located outside the nucleus.
Contribution: Put forward the concept of a nucleus. The whole mass of an atom, or all the positively charged atoms are contained within a small space, later know to be the nucleus. -
H.G.J. Moseley (England)
Determined the charges of nuclei of most atoms. Stated that “The atomic number of an element is equal to the number of protons in the nucleus".
Contribution: Recognised the Periodic Table as being based on atomic number rather than atomic mass. -
Bohr (Denmark)
Developed explanation of the atomic structure. His atomic model consists of built up of successive shells of electrons in orbit. Contribution: Expanded on Rutherford’s ‘atomic theory’ and combined it with Planck’s quantum theory. Bohr suggested that outer shells hold more electrons than inner shells. -
James Chadwick (England)
Discovered neutral atomic particle with a mass similar to a proton. This was later discovered to be a neutron.
Contribution: First man to discover the neutral particle- the neutron. Neutrons are contained in the nucleus along with protons.