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100
Democritus's atomic theory. 400BC
When Domocritus first thought about the atom he hypothisized;all matter consists of invisible particles called atoms. All atoms were invisible, and indestructable. Atoms can differ in size, shape, mass, and position. He was the first of most all scientist to know that tiny particles makes up everything that exists.. -
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Aristotle 340BC
Aristotle believed the only four elements were; fire, water, earth, and air. These elements varied because of how moist they were and there temperature. this theory was adopted for nearly 2000 years. Compared to democritus there was more detail in what the atom was made of. -
antoine lavoisier
Antoine Lavoisier came up with the theory of conservation of mass. This showed that atoms (mater) could neither be created or destroyed, which supported the theory of Democritus. He also showed that compounds are combinations of atoms. This theory was adopted in the late 18th century. This was a huge step from previous thoughts on the topic of atoms. -
John Dalton
Dalton put privious ideas and thoughts into one single atomic theory; all atoms of a given element are identical, and that compounds are combinations of elements. Also atoms of different elements can be told apart by their atomic weights. he also questioned chemical changes. His findings led him to hypothesize that elements cancombine at the atomic level in fixed ratios to form compounds.
-His theory was adopted in 1803. -
Henri becquerel
Henri investigated new elements such as uranium and other materials. During his research he radioactivity in uranium.
Date Adopted: 1896 -
Marie & Pierre Curie
Marie and Pierre Curie grew the understanding of radioactivity through their research of radioactive materials. They discovered radium and polonium during there research.
Date Adopted: 1898 -
J. J. Thomson
Thomson created an experiment with a cathode raytube. which formed rays of what seemed to be light. he then held a magnet against the tube and noticed he could bend the rays. The positive end on a magnet atracts negatively charge materials. he concluded there must have been negative particles around the atoms called electrons.
Date Adopted: 1898 -
Max Planck
Max planck created the quantum theory which explains the nature and behavior of matter and energy on the atomic and subatomic level, which was later used by Niels Bohr to create his model of the atom.
Date adopted:1900 -
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Robert millikan
Robert Millikan discovered the exact charge of the electron in his “Oil Drop Experiment”, He performed this experiment with the help of Harvey Fletcher, but millikan got the credit.
.Date Adopted: 1908 -
ernest rutherford
Ernest Rutherford performed an experiment where he shot alpha particles at gold foil, expecting them to pass right through. Some bounced back causing him to wonder. he figure most of the mass of the atoms must be in the center. with his theory he came up with the planetary model. He was the first person to go inside the atom and wonder what it consists of.
Date model was adopted: 1909 -
niels bohr
Bohr agreed with plancks quantum theory that stated that electrons had quantified amounts of energy. He proposed a new model of the atom where the electrons travel around the nucleus in orbits determined by their energy levels.
Date adopted: 1913 -
Henry Moseley
Moseley first set out to improve the x-ray spectrometry, which had only recently been introduced. However he continued on to study atoms. Moseley is best known for Moseley’s Law which states; that there is a relationship between the energy of a given element and its atomic number (protons). This supported the periodic table and Bohr’s model of quantized energy that followed in latter years.
Adopted in: 1915 -
Erwin Schrodinger
Erwin Schrodinger created the Schrodinger equation, which allowed the motion of the electron to be determined more accurately. This increased the accuracy of Bohr’s model.
Date Adopted: 1926 -
Werener Heisenberg
Heisenberg created the new theory that instead of energy levels that electrons orbited on, there was just a cloud were they occur, and that you can not predict there location, which took away the accuracy of Bohr’s model.
Date Adopted: 1927 -
James chadwick
Chadwick discovered the neutrally charged called the neutron, this discovery gradually led to the atomic bomb. He bettered Bohr’s model by adding neutrons to the nucleus instead of just protons.
Adopted: 1931
