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375
Aristotle
Greek philosopher Aristotle, felt that different substances were made of earth, fire, air, and water. Aristotle did not have an atomic model because he thought atoms did not exist. -
400
Democritus
Greek philosopher Democritus first suggested that all substances consisted of tiny indestructible particles called atoms. -
Antoine Lavoisier
Antoine Lavoisier provided the formula for the protection of matter in chemical reactions. He also discovered the difference between an element and a compound. -
Coloumb
Coloumb formulated the Coulomb's law. The law states that the force between two electrical charges is proportional to the product of the charges and inversely proportional to the square of the distance between them, one of the main forces involved in atomic reactions. -
John Dalton
John Dalton’s atomic theory proposed that:
• all matter consisted of tiny particles called atoms
• atoms could not be divided into smaller particles
• atoms of the same element were alike
• atoms combined in simple whole number ratios. -
Crookes
Crookes created the Crookes’ tube. He demonstrated that cathode rays travel in straight lines and produce phosphorescence and heat when they strike certain materials. -
Sir J.J Thomson
Sir J. J. Thomson explained that the atom contained negatively charged particles called electrons. His model suggested that atoms were positively charged spheres with negatively charged
electrons embedded in them like the
fruit in a plum pudding. -
W.K Roentgen
W.K. Roentgen discovered x-rays when he was experimenting with cathode-ray tubes. -
Becquerel
Becquerel discovered radioactivity. He discovered radioactivity when he was investigating uranium and other radioactive substances. -
Marie Curie
Marie Curies discovered radium and polonium. He discovered radium and polonium when they started to investigate radioactive substances -
Max Planck
Max Planck originated the quantum theory. -
Albert Einstein
Albert Einstein postulated that light was made up of different particles that, in addition to wavelike behavior, demonstrate certain properties unique to particles. He also brought forth the theory of relativity. -
Robert Millikan
Robert Millikan discovered the electric charge of the electron -
Lord Rutherford
Lord Rutherford proposed that the atom consisted mostly of empty space with a dense nucleus containing positively charged protons in the centre. Negatively charged electrons orbited the nucleus. Although Lord Rutherford’s model of the atom was essentially the same as today’s accepted model, its one flaw was that it proposed that the orbiting electrons would eventually lose energy and spiral in towards the nucleus. -
Niels Bohr
Niels Bohr, a scientist who had studied with Rutherford, modified the eve model by suggesting that electrons orbit the nucleus at different energy levels. Only electrons with specific amounts of energy could exist at each level. His model proposed that electrons could move from one level to another by gaining or losing ‘packets’ of energy. Although Bohr’s model explained why electrons did not spiral in towards the nucleus, it did not explain all of the known properties of atoms. -
Geiger
Geiger introduced the first detector of alpha particles and other radiations. -
Erwin Shrodinger
Erwin Shrodinger introduced the Shroedinger Equation, a wave equation that describes the form of the probability waves that govern the motion of small particles and how these waves are altered by external influences. -
Sir James Chadwick
Sir James Chadwick discovered that the nucleus contained particles called neutrons, as well as positively charged protons. Neutrons had no electric charge and a mass about the same as a proton. -
Otto Hahn
Otto Hahn discovered nuclear fission, in which the nucleus of an atom breaks up into two separate nuclei, while experimenting with uranium. -
Lise Meitner
Lise Meitner worked with Otto Hahn to discover uranium fission. -
Glenn T. Seaborg
Glenn T. Seaborg isolated and identified elements heavier than uranium, and in the process, added elements number 94 - 102, and 106. -
Murray Gell-Mann and George Zweig
Murray Gell-Mann and George Zweig brought forth the idea of "quarks", little bits of matter which when used kind of like building blocks, serve to explain some complex chemical substances..
