The History of the Atomic Theory by

The History of the Atomic Theory by https://padlet.com/2131491/vcasxpu3qf2l en-us 2016-11-10 18:15:25 UTC 2016-11-14 17:51:43 UTC hello@padlet.com 400 BC - Democritus vs. Aristotle 2131491 https://padlet.com/2131491/vcasxpu3qf2l/wish/136836537
Democritus was a Greek philosopher who proposed the idea that matter cannot be infinitely divided into smaller pieces. He named the smallest, indivisible particles "atomos," or "not to be cut."

At the time, Democritus's theory was rejected for those of more popular philosophers, such as Aristotle and Plato. Aristotle proposed the idea that all matter was made up of water, earth, fire, and air; while this theory was wrong, it became widely accepted because of Aristotle's status as a philosopher.

Democritus's theory was ultimately ignored and forgotten for 2,400 years because of its widespread rejection for Aristotle's theory and the fact that it could not be tested at the time.

(Class/Quizlet Notes, https://goo.gl/KUjbP7, https://goo.gl/CqYH1A)

]]> 2016-11-10 18:22:12 UTC https://padlet.com/2131491/vcasxpu3qf2l/wish/136836537 1803 - Dalton's Theory of the Atom 2030141 https://padlet.com/2131491/vcasxpu3qf2l/wish/136837262

British chemist John Dalton established the first major atomic theory,

which would later be built upon and modified for future versions of the atomic theory. The major concepts of his atomic theory were:

- All elements are composed of small particles called "atoms."
- The atoms of an element are all identical to one another.
- In chemical reactions, atoms are neither created nor destroyed.
- The same amount of elements are contained in compounds.
- There is no such particle smaller than an atom; "Billiard Ball" model, where the atom is a solid, round sphere.

(Class/Quizlet Notes, https://goo.gl/42W4P)

]]> 2016-11-10 18:23:47 UTC https://padlet.com/2131491/vcasxpu3qf2l/wish/136837262 1897 - J.J. Thomson's Plum Pudding Atomic Model 2030141 https://padlet.com/2131491/vcasxpu3qf2l/wish/136837438

J.J. Thompson had an idea that smaller molecules make up an atom. Thompson found out that when an electric current passes through a gas it gives of particles that are negatively charged. J.J. Thompson is credited with the discovery of the electron.

Thomson realized that the negative charges came within the atom and this particle had to be smaller than an atom. Thomson came to the conclusion that since the gas was neutral then there had to be particles inside the atom that were positively charged. Thompson never found the positively charged particles.

In Thompson's model showed that atoms were made from a substance that was positively charged and included electrons scattered around.

(Class Notes/https://docs.google.com/presentation/d/1Zu1pMqIK1-8-qJWNarYUHprYECrJvPBVULCDGseazZM/edit#slide=id.p41)]]> 2016-11-10 18:24:09 UTC https://padlet.com/2131491/vcasxpu3qf2l/wish/136837438 1911 - Rutherford's Gold Foil Experiment and Atomic Model 2030141 https://padlet.com/2131491/vcasxpu3qf2l/wish/136837691

Rutherford did an experiment where he fired small positively charged particles at a sheet of gold foil that was 2000 atoms thick. In this experiment most of the positively charged particles went through the foil without problem. Some of the particles that were fired instead bounced back. Rutherford knew that positive charges repel each other so if most of the particle that were fired went through the foil then the atom could not be a positive substance. Instead Rutherford discovered that an atom has a positive center called the nucleus. Rutherford is credited with the discovery of the nucleus.

Rutherford's Model

(Notes/https://docs.google.com/presentation/d/1Zu1pMqIK1-8-qJWNarYUHprYECrJvPBVULCDGseazZM/edit#slide=id.p45]]> 2016-11-10 18:24:44 UTC https://padlet.com/2131491/vcasxpu3qf2l/wish/136837691 1913 - Bohr's Atomic Theory 2030141 https://padlet.com/2131491/vcasxpu3qf2l/wish/136838049 Bohr's Theory was that the electrons are on a specific energy level and move an orbit around the nucleus. Bohr's model showed electrons on energy levels with a nucleus in the center.

(Class/Quizlet notes, https://goo.gl/4xD235)]]> 2016-11-10 18:25:25 UTC https://padlet.com/2131491/vcasxpu3qf2l/wish/136838049 Modern "Electron Cloud" or "Quantum" Atomic Theory 2030141 https://padlet.com/2131491/vcasxpu3qf2l/wish/136838166

The Quantum Atomic Theory is also known as the Wave Model and is based on the principles of quantum wave mechanics. This theory states that electrons do NOT move in a definite path. The possible locating of an electron depends on how much energy the electron has and it is impossible to say exactly where an electron is located in an atom. The amount of energy in an electron also determines where it is in the electron cloud. Electrons with the most energy are found the furthest away from the nucleus. Electrons with the least energy are found closest to the nucleus.

Electrons are actually in clouds or orbitals and move about the nucleus billions of times per second. The electrons are not moving around in random patterns.

(Notes/ https://docs.google.com/presentation/d/1Zu1pMqIK1-8-qJWNarYUHprYECrJvPBVULCDGseazZM/edit#slide=id.p54)

]]> 2016-11-10 18:25:39 UTC https://padlet.com/2131491/vcasxpu3qf2l/wish/136838166 1785 - Antoine Lavoisier's Law of Conservation of Mass 2030141 https://padlet.com/2131491/vcasxpu3qf2l/wish/136840718

Antoine Lavoisier, a French nobleman and chemist, is credited for discovering the Law of Conservation of Mass through extensive experimentation. The Law of Conservation of Mass states that mass is never created nor destroyed, but changed to a different form.

(https://goo.gl/C6do9P, https://goo.gl/27sdmu, Quizlet Notes)

]]> 2016-11-10 18:31:32 UTC https://padlet.com/2131491/vcasxpu3qf2l/wish/136840718 1794 - Joseph Proust's Law of Constant Composition 2030141 https://padlet.com/2131491/vcasxpu3qf2l/wish/137072646

The actor and French chemist, Joseph Proust, is credited as discovering the Law of Constant Composition. This law details that compounds always contain the same proportion, by mass, of elements.

(Quizlet Notes, https://goo.gl/gaOj6b, https://goo.gl/x6Cvn)

]]> 2016-11-11 18:36:25 UTC https://padlet.com/2131491/vcasxpu3qf2l/wish/137072646 1932 - James Chadwick's Discovery of the Neutron 2030141 https://padlet.com/2131491/vcasxpu3qf2l/wish/137076382

The English physicist James Chadwick is credited with the discovery of the neutron, one of the subatomic particles contained within the nucleus of an atom. He developed this conclusion based upon the results of experimentation conducted by Frédéric and Irène Joliot-Curie. The Joliot-Curies performed an experiment which resulted in protons being knocked back from paraffin wax by using polonium and beryllium as a source for what the two supposed was gamma radiation.

(Quizlet Notes, https://goo.gl/qoxGk, https://goo.gl/u5Lhuw)

]]> 2016-11-11 18:52:51 UTC https://padlet.com/2131491/vcasxpu3qf2l/wish/137076382