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335
Aristotle
Click here to see Aristotle's "atomic" model.
(384- 322BC)
Aristotle did not believe in the atomic theory and so he taught otherwise.He thought everything was made up of the four elements, earth, fire, water and air. He believed all substances were made up of different amounts of these things. Most people followed this idea rather than Democritus' idea which is why it was overlooked for about 2000 years. -
465
Democritus
Click here to view Democritus' atomic model.
(460 to 370BC)
Democritus’ atomic model is the earliest atomic model. He was the first to use the term atom and proposed that atoms were mechanically bound. He stated that atoms are indestructible, atoms are solid but invisible, solids are made of small, pointy atoms, liquids are made of large, round atoms and oils are made of very fine, small atoms that can easily slip past each other. -
John Dalton
Click here to view John Dalton's atomic model.
(1766 -1844)
Wasn't until almost two millennia after Democritus suggested the existence of the atom that it was revisited. Daltons theory was that all matter is made of atoms, atoms are indivisible and indestructible, all atoms of a certain element are identical in mass and properties, compounds are made when two or more different atoms combine and a chemical reaction occurrs when atoms rearange. Since these theories things have canged and adapted but the essence still remains. -
Micheal Faraday
(22nd of September 1791 - 25th of August 1867)
Micheal Faraday made one of the most signifigant discoveries thatled to the idea that atoms had an electrical component. It was clear to him that electrical forces joined atoms into compounds and held atoms together. -
William Crookes
(1832 - 1916)
William Crookes loved maths and science during his school years. He identified many properties of cathode rays. He discovered that the rays move in straight line, cause glass to glow, carry negative charges and are capable of being deflected by electric fields. His discoveres directly influenced the discoveries of electrons by Joseph John (J.J) Thomson. -
Dmitri Mendeleev
Click here to view the first Perodic Table made by Dmitri Mendeleev
(8th of February - 2nd of February 1907)
Dmitri arranged the elements in order of increasing atomic mass.This arrangement is now the basis of the current periodic table. His table had three blank spaces where he predicted three unknown elements would go. They turned out to be germanium, gallium and scandium. -
Joseph John (J.J.) Thomson
Click here to view Joseph Thomson's atomic model.
(18th Dec 1856 - 30th of Aug 1940)
Joseph Thomason discovered the electron. He put forward a new theory that atoms were made up of small particles. He proved his theory by using a cathode ray tube. From this he developed an atomic model, generaly know as the ‘plum pudding’ model. The ‘Plum Pudding’ Model is shown as a positively charged sphere (pudding) with smaller negatively charged electrons inside (dotting raisins). -
Ernest Rutherford
(30th of August 1871 - 19th of October 1937)
Ernest Rutherford took the theory of Hantaro Nagaoka but tweaked it slightly. He claimed that the central nucleus was positively charhed and the orbiting electrons were negatively charged. This suggested that most of the mass of the atom was contained in the nucleus and the rest was mainly empty space. -
Eugen Goldstein
(5th of September 1850 - 25th of December 1930)
Eugen Goldstein discovered protons when conducting a Anode Ray experiment. According to Goldstein atoms contain positively charged particles called protons. He said that since atoms contain negatively charged particles, they must contain positively charged particles as well for them to be electrically neutral. -
Hantaro Nagaoka
(15th of August 1865 - 11th of December 1950)
Hantaro developed an atomic model based on the way the planets orbited the sun. In the centre there was the nucleus (the sun) and electrons revolved aroud the nucleus bound by electrostatic forces (the planets). This theory was successfully confirmed by Ernest Rutherford but with some alterations. -
Robert Millikan
(22nd of March 1868 - 19th of December 1953)
J.J Thomson had already discovered the charge to mass ratio but the actual charge and mass values were unknown. Considering the ratio was already discovered, only one of the two values had to be discovered and the other could just be calculated. Milikan worked on an oil drop experiment where it measured the charge of a single electron. This device was able to figure our the charge. -
Henry Moseley
(23rd of November 1887 till the 10th of August 1915) Mosely’s discovery showed that atomic numbers have strong physical basis. These numbers helped sorting the elements, especially in the periodic table. Simple modifications of Bohr’s formulas were found to give Moseley theatrical justification for determining atomic numbers. -
Niels Bohr
Click here to view Niels Bohr's atomic model
(7th of October 1885 - 18th of November 1962)
Neils Bohr’s research led him to the discovery that atoms give off electromagnetic radiation. This is the result of electrons jumping to different orbit levels around the core nucleus. His discovery formed the basis of atomic research for other future scientists. Today, his model is still the most widely accepted. -
James Chadwick
(20th of October 1891 - 24th of July 1974)
James Chadwick worked under Ernest Rutherford at Cambridge. He proved the existence of nutrons, particles without any electrical charge. He realised that neutrons where also found in the nucleus as well as protons. -
Werner Heisenberg
Click here to view Werner Heisenberg's atomic model.
(5th of December 1901 - 1st of February 1976)
Werner Heisenberg said that electrons do not travel in neat orbits rather in an electron cloud, wildly spreading and moving around. Werner calculated the behaviour of electrons and subatomic particles (particles that also make up an atom). His work was influenced by math. He used mathematics to understand the patterns of an atom’s electrons rather then scientific terms. Werner’s discovery helped clarify the modern view of the atom
