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350
Aristotle
350 BC – Aristotle disbelieved the ancient Greek theory of atoms being of different sizes, regular geometric shapes and being in constant motion. He didn't think atoms could be in constant motion in a void. He developed the theory that all matter consisted of four elements: Earth, Air, Water and Fire. There were also four qualities: dryness, hotness, coldness, and moistness. Fire was dry and hot; water was moist and cold, etc. His theory was used for almost 2000 years. -
442
Democritus
- "by convention bitter, by convention sweet, but in reality atoms and void.” Democritus was a Greek philosopher who developed the atomic theory of the universe. His atomic theory anticipated the modern principles of the conservation of energy and the irreducibility of matter.
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Isaac Newton
Proposed a universe that was made of small particles in motion stating that "matter is formed of solid, massy, impenetrable particles" -
Antione Lavoisier
He found and termed both oxygen (1778) and hydrogen (1783), helped construct the metric system, put together the first extensive list of elements, and helped to reform chemical nomenclature. He was also the first to establish that sulfur was an element (1777) rather than a compound. He discovered that, although matter may change its form or shape, its mass always remains the same. Lavoisier could not entirely escape from Aristotle’s influence. The second element in -
John Dalton
Was a British chemist and physicist, who developed the atomic theory upon which modern physical science is founded. Dalton's most important contribution to science was his theory that matter is composed of atoms of differing weights and combine in simple ratios by weight. Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. -
J.J. Tompson
Tompson demostrated that atoms are actually composed of aggregates of charged particles. He did this by using Cathode rays which was when the two charged were together a current would be formed which is cathode rays this was to show the charge/ mass of electron. Of course he was the founder of electrons. the very large e/m of the electron is due to an ordinary charge and a very small mass, much smaller than that of the lightest atom. Contributions atom containing positve and negative particles. -
Max Planck
Max Planck was the founder of the Quantum theory. The Quantum theory has revolutionised our understanding of atomic and sub-atomic processes. Planck also created Planck’s Law of Black-body Radiation ( the intensity spectrum of electromagnetic radiation from a black body at temperature). -
Hantaro Nagaoka
Nagaoka's 'Saturnian' model of the atom. Nagaoka creates a 'Saturnian' model of the atom with flat rings of electrons revolving around a positively charged particle. This model assists scientists in gaining a clearer mental image of the composition and structure of the atom and further develops their understanding of the electrons' positioning around the atom and atomic electrical charge.This model is later proven to be incorrect, due to the inaccurate size of the nucleus. -
Neils Bohr
Neils explained that electrons travel around the nucleus in exact paths. These paths are always at a certain level away from the nucleus. He also stated that electrons cannot travel in between each path, but they can hop from one path to another.Conclusion- electrons travel in paths around the nucleusContribution- electron paths -
Henry gwyn-Jeffreys Mosely
Henry Gwyn-Jeffreys Moseley arranged the periodic table by their atomic numbers and used X-ray tubes to determine the charges in the nuclei of most atoms. He experimentally demonstrated that the major properties of an element are determined by the atomic number, not by the atomic weight, and established the relationship between atomic number and the charge of the atomic nucleus. -
Ernest Rutherford
Rutherford discovered the proton while undergoing an nitrogen gas experiment that involved some alpha particles showed that the nitrogen atom broke down under great force from collision and the particle found was part of its nucleus. Rutherford used nitrogen gas and alpha particles to collide under great force and what was left was part of a particle from the nucleus of the nitrogen atom. Rutherfords contribution is that he discovered the proton. -
James Chadwick
James Chadwick used the alpha particles to discover a neutral atom particle with a mass close to a proton – thus discovered the neutron.. His discovery formed the base for the investigation of the tougher questions of nuclear physics: the nature of the nucleus and its forces.
