Justin Walton Question 1A

-Democritus- He said that everything is composed of indivisible atoms. He said that there is an infinite number of kinds of atoms, and this is why there are differences in the physical matter in our world.

John Dalton- He is credited with developing the first atomic theory that said all matter is made up of atoms, and that all atoms of the same element are identical. The atoms of different elements are different. He also said that atoms can't be created nor destroyed. His work helped to arrange atoms by atomic weight like they are in the current periodic table.

Mendeleev- He discovered that when elements were arranged in order of increasing mass, there was a pattern in elements that were vertically alligned. He discovered this by using cards with element names and various properties listed on them. He would arrange them according to certain characteristics, and on one of these arrangements he noticed a pattern.

J.J. Thomson- Thomson made a groundbreaking discovery in the development of the atomic model when he discovered electrons. He discovered this through his cathode ray experiment. He found that the rays could be deflected by an electric field, and used the deflection to determine the particle's mass. He discovered a particle 2000 times lighter than hydrogen and determined that it was negatively charged.

Rutherford- Rutherford performed the gold foil experiment. He hypothesized that atoms were composed of both positive and negative charges. He then shot alpha particles at a very thin sheet of gold foil and noticed that while most passed straight through, a small amount were deflected. He determined that they were hitting a large positive mass which later became known as the nucleus. He is credited with discovering the proton.

Niels Bohr- He composed the Bohr model of the atom. This described atoms as having small positively charged nucleus' and electrons that orbit in perfect circles, similar to the Solar System. Bohr made many contributions in the development of the atomic bomb.

Moseley-He devised a periodic table sat up by atomic number rather than atomic mass. He also determined a way for the number to be mathematically figured rather than just represent the place the element is on the table. This allowed scientist to understand physical makeup of atoms and develop a better model for the atom.

Chadwick- He is credited with the discovery of the neutron. he discovered this by colliding berrylium atoms which released massive neutral particles. His discovery made it possible for later scientists to construct new elements in the lab.

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