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500
Democritus - Greece
http://www.timelineindex.com/content/view/1228 http://abyss.uoregon.edu~js/21st_century_science/lectures/lec05.html Democritus theorized that all matter (plus space and time) is composed of tiny indestructible units, called atoms
Introduced the idea of matter and atoms. This contributed to our understanding of the atom as he introduced the initial idea of matter and atoms -
Newton - England
http://www.cartage.org.lb/en/themes/sciences/physics/atomicphysics/atomicstructure/atomictimeline/atomictimeline.htm' Anticipated a mechanical universe with small solid masses in motion. He stated that "matter is formed of solid, massy impenetrable particles”. From Newton's theory, we discovered that motion is involved with the particles that form matter. It also assisted other scientists, including Rudier Boskovic to build on their atomic theories. -
Dalton - England
http://www.timelineindex.com/content/view/1474
Dalton constructed a model based on observations of pure substances. He stated that matter was made of tiny indivisible particles, which he named atoms. He said that atoms could join together to form molecules in a regular predictable way. Dalton also developed a system of chemical symbols and arranged them into a table. He then theorised that compounds were made up of molecules, and that molecules are composed of atoms in definite proportions. -
G.J. Stoney - Ireland
G.J. Stoney discovered that electricity was made of discrete negative particles he called "electrons". He also estimated the number of molecules in a cubic millimetre of gas, at room temperature and pressure.
Dalton made a great contribution to the atomic theory. He came up with the idea that the electron is an important part of the atomic theory as well as contributing to the theory of gasses.
http://www.cartage.org.lb/en/themes/sciences/physics/atomicphysics/atomicstructure/atomictimeline/a -
J.J. Thomson - Britain
http://www.timelineindex.com/content/view/1611'
In 1897 in Cambridge, J.J Thomson experimented on cathode rays. Britain physicists had argued that these rays were particles, but German physicists disagreed, believing that they were a type of electromagnetic radiation. Thomson showed that cathode rays were particles with a negative electric charge and that they were much smaller than an atom. He also thought all atoms contained them. These particles were later named electrons. -
Planck - Germany
http://www.cartage.org.lb/en/themes/sciences/physics/atomicphysics/atomicstructure/atomictimeline/atomictimeline.htmMax Planck was a German physicist who is considered to be the inventor of quantum theory. In 1899, he discovered a new fundamental constant, which is used, for example, to calculate the energy of a photon. Also that year, he described his own set of units of measurement based on fundamental physical constants. 1 year later, he discovered the law of heat radiation. This law became the basis of quantum theory, which emerged ten years later in cooperation with Einstein and Bohr. -
Nagaoka - Japan
Hypothesized a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle.
The model made two predictions:
The nucleus is big
the electrons that revolve around the nucleus are bound by electrostatic forces
http://www.cartage.org.lb/en/themes/sciences/physics/atomicphysics/atomicstructure/atomictimeline/atomictimeline.htm -
Millikan - USA
http://www.cartage.org.lb/en/themes/sciences/physics/atomicphysics/atomicstructure/atomictimeline/atomictimeline.htmConducted an oil drop experiment, called the "falling drop experiment" which determined the charge and the mass of an electron.
Milikan contributed to the atomic theory by determining the charge and the mass of the electron. -
E. Rutherford - New Zealand
http://www.cartage.org.lb/en/themes/sciences/physics/atomicphysics/atomicstructure/atomictimeline/atomictimeline.htmhttp://www.timelineindex.com/content/view/2416Ernest Rutherford was a chemist and a physicist who became known as the "father" of nuclear physics. He established the orbital theory of the atom by Using alpha particles as atomic bullets and probing the atoms in a piece of thin (0.00006 cm) gold foil. He established that the nucleus was "very dense, very small and positively charged". He also assumed that the electrons were located outside the nucleus. -
H.G.J. Moseley - England
http://www.cartage.org.lb/en/themes/sciences/physics/atomicphysics/atomicstructure/atomictimeline/atomictimeline.htmUsing x-ray tubes, he determined the charges on the nuclei of most atoms. He discovered that the atomic number of an element is equal to the number of protons in the nucleus
His work was used to reorganize the periodic table based upon atomic number instead of atomic mass. -
Niels Bohr - Denmark
http://www.timelineindex.com/content/view/1206' Bohr developed the atomic model we use today, where the atoms are built up of consecutive orbital shells of electrons. He developed on a theory made by Ernest Rutherford by proposing that electrons travel only in certain successively larger orbits.
His theory of electrons travelling in orbits added to the structure of the atom. -
James Chadwick - England
'http://www.timelineindex.com/content/view/2926'
Chadwick discovered a previously unknown particle in the atomic nucleus. This particle became known as the neutron because of its lack of electric charge
Chadwick’s discovery made it possible to create elements heavier than uranium in the laboratory.
