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Aristotle
Aristotle had a unique atomic theory. He didn't believe in atoms. He believed that all matter was made up of 5 elements. Elements are the only surviving part of his theory. The 5 five elements were air, earth, water, fire, and aether. -
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Democritus
Democritus thought that atoms were indivisible and indestructible. He was correct but he did not have any experimental proof. -
Isaac Newton
Newton was knighted in 1705. Isaac Newton had yet another atomic theory. He proposed a mechanical universe made up of small solid masses. These solid masses are constantly moving. This was important because previously we thought atoms were stationary masses. -
John Dalton
John Dalton was an english chemist and teacher. He created his own atomic theory. He stated that all elements were made up of tiny particles called atoms. All atoms that make up an element are all the same. They also all have the same mass. -
J.J. Thomson
J.J. Thomson was the first to use the cathode ray tube on this timeline. He used the cathode ray tube to discover electrons. A cathode ray tube is sealed glass tube with alpha particles in the tube, along with an electrical current. Using magnets he found that the ray was attracted by a positively charged plate, thereby proving that the ray had a negative charge. He, after further experimentation, found that the charge to mass ratio of an electron will always constant. -
Dmitri Mendeleev
Mendeleev was the founder of the periodic table. Periodic table caused by periodic law. He split the elements into 7 groups based on there properties. The elements were also sorted according to there atomic mass on the periodic table. Periodic law states that when you sort elements by their atomic numbers, elements will appear at regular intervals. -
Eugene Goldstein
Goldstein also used the cathode ray tube. he discovered that there were rays traveling the opposite way of the cathode rays. These positively charged particles are called protons. Atoms are electrically neutral so these protons explained the missing link. A proton has a mass of about 1840 times that of an electron. -
Ernest Rutherford
Using the gold foil experiment Rutherford discovered the how atoms were constructed. Unlike Thomson's plum pudding model, Rutherford discovered that an atom had a nucleus made up of protons and neutrons with electrons circling around it. With his gold foil experiment, he shot alpha particles at a piece of gold foil. some the alpha particles hit one of the nuclei of the gold atoms and bounced off, but most just passed right through. This then proved his atomic model. -
Robert A. Milikan
Milikan is the only U.S physicist on our timeline. Milikan used the data Thomson discovered and his own oil drop experiment to find the charge and mass of an electron. The oil drop tested the mass and charge of an electron by using a magnet fields, gravity, and a fine spray of oil. The mass of an electron is 1/1840 the mass of hydrogen or 2,000 times less than a proton. The charge of an electron is 1.60 x 10 to the 19th power. -
James Chadwick
Sir James Chadwick was an english physicist who was knighted in 1945. Chadwick discovered the last piece of the atom. The neutron. The neutron is a neutral particle, hence the name neutron. He found that the mass is nearly equal to that of a proton.
