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200
440 BC- Democritus
Democritus thought that if you keep cutting things in half over and over then you would eventually get something too small to cut. He called this atomos meaning "not able to be divided" in Greek. -
201
350 BC- Aristotle
Aristotle was a Greek philosopher who did not agree with Democritus. He thought it would get smaller and smaller and he was so smart that everyone believed him for a while. Aristotle was wrong, Democritus was right the final particle would be called an atom. -
John Dalton
People had figured out that you can combine elemnets based on porportion. Dalton wanted to know why. He learned they can combine becasue each elemnt is based on an sertant type of atom, He made a theory. First, all substances are made of atoms. Next, atoms of the same element are the same and atoms of diffrent elements are diffrent. Last, atoms join with other atoms to make new substances. -
J.J. Thomson
Thomson proved that Dalton was wrong, there were smaller particles that made up an atom. He learned that with a positively charged plate a beam would be attracted to the plate. He said that the beam had negatively charged particles called electrons. -
Ernest Rutherford (1909)
Rutherford wanted to test Thomson's theory, he shot a beam of positively charged particles at a gold foil. Most of them went straight through but some went in different directions or straight back. This showe that atoms were not blobs, but mostly empty space with highly dense parts. -
Ernest Rutherford (1911)
Rutherford edited the atomic theory, he said that there must be a positively charged middle of the atom, it's diameter 100,000 times smaller than an atom, called he nucleus. He reasoned the positively charged atoms that went near the middle bounced away and the ones that hit bounced right back. -
Niels Bohr
Bohr believed that electrons circled the nucleus in different paths, or energy level, related to light. There was no path between the levels but they electrons could jump from one to another, like a ladder. -
Erwin Schrodinger and Werner Heisenberg
These scientists proved that electrons do not circle in certain paths, and it can not be predicted. There are areas called electron clouds that the electrons are likely to be in.
