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100
Democritus
Democritus, a greek philospher in 460 BC, wondered what would happen if you cut something in half and cut in half, and cut it in half, again and again, until you could not cut it in half anymore. He called this the the smallest piece of something, and dubbed it the atom. -
100
Aristotle
Aristotle dismissed the idea of the atom.He believed that all matter was composed of earth, fire, water, and air. He said that the idea of atoms were impossible, disagreeing with Democritus. Since everyone looked up to Aristotle, everyone soon forgot about the idea of the atom, until the 1800s. -
Antoine Lavoisier
Lavoisier is sometimes called the father of all chemistry. He studied combustion, and thought of things in terms of elements, not atoms. He discovered the law of conservation of mass, when he found the remains of an experiment equaled the combined mass of the two elemetns that he started with. -
John dalton
John Dalton was an english chemist who performed various experiments that showed that matter was made up of small particles (atoms). He didn't know much else, but he thought that the idea was important. He was the first person to think about the atom, since Democritus. This disproved Aristotles doubt of the atom. -
Henri Becquerel
In 1896, Henri Becquerel was studying the properties of x-rays. He wanted to show that uranium absorbed energy from the sun, but he failed. But when he tried to develop the photos with just the uranium, it still worked. Because of this he discovered the radioactive energy that was given off by uranium. -
J.J Thompson
Thompson discovered electrons in 1897 and found out they had a negative charge.He then assumed that matter had a positive charge, which was later diproved. -
Marie & Pierre Curie
The Curie's began to investigate this new source of energy discovered by Henri Becquerel, shortly after it was found. Marie Curie made up the term radioactivity, shortly after they extracted uranium from ore and discovered the ore was more radioactive than the uranium. This led to the discovery of more radioactive elements. -
Max Planck
Planck was a theoretical physics professor in Berlin. By vibrating an atom enough, you can measure the energy only in discrete units.He called the energy packets Quanta. -
Robert Milikan
Millikan was the man who discovered the amount of charge of an electron. Thompson had already discovered the electron, but not the amount of charge it had. Millikan discovered the charge using an oil-drop experiment. After which he easily calculated the mass of an electron -
Ernest Rutherford
Rutherford thought that it would be a good idea to bombard atoms, with alpha rays, particles that had positive charges and were thought to be part of the atom discovered by Thompson.He thought that he could probe the inside of an atom. After the experiment he concluded that there were tiny bits of negative atoms (electrons) orbiting around a large positive matter (nucleus). -
Niels Bohr
Bohr was a Danish physicist, who said that to find out why the electrons don't spiral into the nucleus we must disregard the theories that say they should. He came up with the bohr model, as seen in the image above. The bohr model was constantly expanded to accomadate further scientific discoveries on the atom. -
Henry mosely
Mosely studied under Ernest Rutherford and assisted with research on x-rays. He developed the system of the elements on the periodic table ranging from lowest atomic number to highest number. He made the periodic table much easier to understand -
Rutherford cont.
In 1919 Rutherford finally identified the particles of the nucleus as discrete positive charges of matter, He knocked out atoms inside the nucleus of a few elements with alpha particles and saw that they had positive charge. He named the protons, from a greek root. However, it disagreed with magnetism, because opposite charges normally attract each other but, the electrons are repulsed by the nucleus. -
Werner Heisenberg
Heisenberg had a theory of his own called matrix mechanics which also explained the behavior of atoms. It differed from schrodingers wave mechanics, in the fact that it used matrices. they were both mathmatically correct. Heisenberg came up with an uncertainty principle, in which said that no experiment can measure the position and momentum of a quantum particle simultaneously. -
Erwin Schrodinger
Schrodinger took the idea that light acted like both particles and waves, and applied it to atoms. He formed an atom model, based on this idea. The vibrations on them constantly traveled in circles. Another scientist later thought that, the atoms were waves when traveling through space and particles when moving in circles. -
James Chadwick
Chadwick was the man who finally discovered the neutron. He found it because it weighed an incredibly small fraction more than a proton. Since it was in the center with the protons, the center was called the nucleon.
