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400 B.C. -Democrtius
(B.C) Democritus was a Greek philosopher. He wanted to learn what the universe was created out of. So, he decided to find out. He believed that matter can be cut up until it is the size of an atom, which is indestructible. He also thought that an atom looked like a billiard ball, and is invisible to people and is impossible to be seen. He had some important experiments. "What he did was take a simple seashell and break it in half. He then took that half and broke it in half until it was an atom. -
Dalton's Model
After about 2400 years of ignoring that theory, a single man realized the importance of Democritus's theory. His name was John Dalton. Dalton was an Emgish chemist who performed many experiments to prove that atoms indeed exist. He also believed the atpom was a solid ball, and was homogenerous, so the mixture inside was not visible. He performed many experiments which led the majority of the population to believe him. One of his findings were that all atoms f the same matrerialare the same, -
Thompson's Model
Thompson believed in atoms, but thought it wasn't like a billard ball. Instead he thought negatively charged substances were floating around in a positively charged substance. These negatively charged substances were descovered when during an experiment, Thompson combined electricity smd gas, and it gave him a small current. This inspire him to continue looking, and ultimately led to the discovery of the electron, which helped in later studies on the atom. But, the nuculeus wasn't discovered. -
Rutherford's Model
An English physist named Ernest Rutherford fired a stream of positive particles and a gold sheet 2,000 atoms thick. Some of these particle passed straight through the sheet and others bounced off. Using these results, Rutherford concluded that there was a postively charged, dense center in an atom, almost like a core. He decided to call that core the 'nucleus'. In his diagram/model of an atom, there are negativly charged particles scattered around the atom's edge. -
Bohr's Model
A Danish man named Niels Bohr created ANOTHER model for the atom. But unlike other models where the electrons are just scattered around, he organized them by energy levels. He also figured out that the nucleus is made up of protons positivly charged) and nutrons (not charged. In his model, each electron orbits around the atom's nucleus,almost like the planets orbit the sun. But, the electron's orbit paths intersect at many places. Almost 100 years later, a new type of atom model is created... -
Modern Model
Now, here we are. The modern atom model. This has many things from the Bohr model, except put together differently. There is the nucleus, like in the Bohr model. But, the electrons aren't shown with orbit paths. people learned that orbit paths are not always followed exaclty. So, there ius a yellow cloudish circle surrounding the nucleus. That is the spot were electrons are likely to be spotted. Like the Bohr model, the location of the electrons depends greatly on their energy levels.
