History of Atomic Theories by Alexandra Papadiamantis

History of Atomic Theories by Alexandra Papadiamantis https://padlet.com/211476/r58fmilyb6ie en-us 2016-11-10 18:22:05 UTC 2025-10-23 11:58:52 UTC hello@padlet.com https://padlet-assets.s3.amazonaws.com/icons/Rafaelo.png Democritus vs Aristotle 211476 https://padlet.com/211476/r58fmilyb6ie/wish/136837564 Democritus
In 400 BC, Democritus proposed a theory that there was a particle called, "atomos." Democritus said that the atoms were hard, very tiny and all made out of the same material. He also thought that there was an infinite number of atoms of all different sizes.
(Democritus link & Notes)
Aristotle
In 300 BC, Aristotle believed that water, air, fire and earth were the elements that made up everything in the world. (Notes)
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]]> 2016-11-10 18:24:28 UTC https://padlet.com/211476/r58fmilyb6ie/wish/136837564 Dalton's theory of the atom 211476 https://padlet.com/211476/r58fmilyb6ie/wish/136838241 In the 1800's, Dalton claimed that all atoms were invisible and indestructible particles that make up the universe. Atoms were small, hard and all atoms of elements are the same. Dalton also figured out a compound, which is one or more molecules put together. ]]> 2016-11-10 18:25:47 UTC https://padlet.com/211476/r58fmilyb6ie/wish/136838241 JJ Thomson’s plum pudding theory of the atom 211476 https://padlet.com/211476/r58fmilyb6ie/wish/136838732

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In 1987, Thomson proposed a theory that atoms were made of smaller particles. He later on did an experiment, electric current passed through gas. The result was negatively charged particles, which were electrons. He had discovered the electron! Thomson contemplated a model of an atom that he thought looked like a "Plum Pudding." (Notes)

]]> 2016-11-10 18:26:47 UTC https://padlet.com/211476/r58fmilyb6ie/wish/136838732 Rutherford's theory of the atom after the famous gold foil experiement 2036681 https://padlet.com/211476/r58fmilyb6ie/wish/136838820 After the famous gold foil experiment, Rutherford made conclusions that made no other had made before. He noticed that some of the Positive "bullets" bounced back in the direction they were shot while most just went through the foil. He concluded that most an atom is made up mostly open space, the "nucleus" (which he called it) repelled the positive particles which he shot at it. He also inferred that the nucleus was tiny compared to the rest of the atom. Rutherford called the center of the atom where all the positively charged particles were contained while the negative particles were around the outside edge of the atom. (Notes)

https://en.wikipedia.org/wiki/Rutherford_model ]]> 2016-11-10 18:26:59 UTC https://padlet.com/211476/r58fmilyb6ie/wish/136838820 James Chadwick 211476 https://padlet.com/211476/r58fmilyb6ie/wish/136839002 In 1932, Chadwick conducted an experiment. Alpha particles and Beryllium were put together to see what the result would be. At first Chadwick thought the result was gamma rays and put a piece of paraffin wax paper in front to see if that changed anything. After the experiment, he realized that the charge was neutral and that he had discovered a neutron.
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Discovered the neutron]]> 2016-11-10 18:27:22 UTC https://padlet.com/211476/r58fmilyb6ie/wish/136839002 Bohr's theory of the atom 2036681 https://padlet.com/211476/r58fmilyb6ie/wish/136841500 Niels Bohr, in 1913, purposed the idea that each electron had a specific level of energy. He also noticed that the electrons move in an "Orbit" around the nucleus like planets to the sun. The orbits are also referred to as energy levels that are located a specific distance away from the nucleus. (Notes) https://www.britannica.com/science/Bohr-atomic-model]]> 2016-11-10 18:33:21 UTC https://padlet.com/211476/r58fmilyb6ie/wish/136841500 Modern “electron cloud” or “quantum” theory of the atom 2036681 https://padlet.com/211476/r58fmilyb6ie/wish/137069354 This theory states that electrons in an atom do not follow a specific path like Bohr believed. The only way to relatively know where the electron is to know the energy level. This theory is the one that is accepted today and also states that the atom is made of a small positiely charged center and enough electrons in the "cloud" surrounding it to make the atom neutral and stable. (notes)

http://www.universetoday.com/38282/electron-cloud-model/]]> 2016-11-11 18:20:57 UTC https://padlet.com/211476/r58fmilyb6ie/wish/137069354 Joseph Proust 211476 https://padlet.com/211476/r58fmilyb6ie/wish/137250368 In 1794, Joseph came up with the Law of Definite Proportions. This law stated that every element always will contain its component elements. The component elements are measured in mass.
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]]> 2016-11-14 01:44:56 UTC https://padlet.com/211476/r58fmilyb6ie/wish/137250368 Robert Millikan 2036681 https://padlet.com/211476/r58fmilyb6ie/wish/137261737 In 1909, Robert Millikan discovered the weight of an electron. He used the ratio formula that was know in his oil drop experiment to find that each negative particle weights (9.11x10^-28g). (Notes)

http://uudb.org/articles/robertmillikan.html]]> 2016-11-14 03:58:18 UTC https://padlet.com/211476/r58fmilyb6ie/wish/137261737