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400
Democritus 460 B.C
Democritus claimed that everything is made up of atoms. He said atoms could be physically divided but no geometrically. He claimed atoms were constantly moving and there are an infinite number of them. He said atoms are indestructible and always will be. He declared atoms come in different shape, size and mass. He thought the solidness of a material coincided with the shape of the atom. -
400
Aristotle 384 B.C
Aristotle stated that all matter is made up of the four elements: fire, water, earth and air. His statement was quite generalized and did not come from evidence rather from theories and religious beliefs. There were also four qualities for the elements: dryness, hotness, coldness, and moistness. Aristotle also believes there were two forces: harmony and conflict. Each element is aligned to on of these forces and was suppose to naturally move into their rightful place. -
Antoine Lavoisier 1743-1794
The “father of chemistry”, Antoine Lavoisier discovered that water was made up of oxygen and hydrogen and he also showed that chemical elements could not be created or destroyed but combined into different compounds. John Dalton’s work was based upon Antoine Lavoisier.Lavoisier showed that diamonds and graphite were both made from carbon by burning them both to create carbon dioxide. He also presented that a candle burning and a person breathing both exhaled carbon dioxide. -
John Dalton 1766-1844
John Dalton said that there was a point where matter could not be broken down any more. He named these particles atoms. He proposed elements are made up of atoms. Atoms cannot be created or destroyed in a chemical reaction. Atoms of a specific element are identical. -
James Chadwick 1891-1974
James Chadwick was the discoverer of the neutron. His experiment was to bombard a thin sheet of beryllium with alpha particles. After the experiment he found that the gamma rays emitted from the beryllium contained a third subatomic particle, the neutron. -
J.J Thomson 1856-1940
JJ. Thomson put forward the atomic model based upon a “plum pudding”. In the model the volume of the atom is made up of positive protons, which is represented as the pudding. The small electrons are spread out inside the atom to keep the atom at a neutral charge. The electrons are represented as the raisins/fruit inside the pudding. -
J.J Thomson 1856-1940
Plum Pudding Model -
Robert A. Millikan 1868-1953
Robert A. Millikan conducted a test in which he was to try to find the electric charge of an electron. He sprayed tiny drops of oil through a charged hole in an enclosed area. The oil was now charged. He then turned on an electric field and was able to move the drops of oil up and down as he wanted. From this he was able to observe the speed of the particles and figure out the charge of an electron; 1.6*10-19 Coulombs. -
Johannes Geiger 1882-1945
Johannes Geiger was the co creator of the Geiger counter. The Geiger counter is a machine that measures the number of alpha particles and other ionising radiation. All his work also helped the lead up to Ernest Rutherford’s theory of the atom. -
Francis Aston 1877-1945
Francis Aston invented the mass spectrograph. This device measures the concentration of atoms and molecules. He was also the first person to observe an isotope. He saw that there were three different kinds of hydrogen atoms. Hydrogen atoms usually have a mass number of 1 he observed they could also have 2 or 3. His work led Rutherford to predict the existence of the neutron. -
Ernest Rutherford 1871-1937
Ernest Rutherford performed an experiment to test the volume of the atom. He fired alpha particles at a thin sheet of gold foil He found that only some of the particles rebounded back. The rest went straight through the gold. This proved that the mass of an atom is located at its nucleus, which is positively charged. The rest of the atom is empty space occupied by the electrons. He also proposed the existence of third atomic particle, the neutron. -
Niels Bohr
Niels Bohr created an atomic model where the nucleus of the atom is made up of protons and neutrons. Electrons that travel in a circular motion orbit around and surround the nucleus. His atomic model resembles the solar system but is held together by force of attraction not gravitational pull. -
Louis de Broglie 1892-1987
Louis de Broglie proposed that electrons act like both particles and waves. This explains that electrons move randomly around the atom and not in a circular orbit like originally thought. This also explains the random movements that electrons make that we weren’t able to explain before. -
Erwin Schrodinger 1887-1961
Erwin Schrodinger stated that rather than electrons being in set positions of eh electron configuration they have a more random placement. He devised a new atomic model. He used mathematical equations to show where most likely an electron will be. An electron cloud surrounds the nucleus that shows the possibilities of where an electron could be placed. Where the cloud is densest it is most likely to have an electron. In less dense areas there is less chance of containing an electron. -
Werner Heisenberg 1901-1976
Werner Heisenberg was able to calculate the movement and behaviour of an electron. He also proposed the uncertainty theory, which states that you cannot simultaneously calculate the momentum and position with high precision. -
Murray Gell-Mann 1929-?
Merray Gell-Mann showed people what makes up protons and neutrons, quarks. A quark is a fast-moving point of energy and every proton and neutron has 3. There are two types of quarks up quarks and down quarks. Up quarks have a positive charge and down quarks have a negative charge. . The charge of the quarks makes up the electrical charge of the nucleus. Protons contain two up quarks and one down quark, while neutrons contain two down quarks and one up quark. This makes neutrons have its negative -
J.J Thomson 1856-1940
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J.J Thomson 1856-1940
