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440BCE- Democritus
He thought he could eventually cut a particle into 2 parts and you would eventually end up with a particle that could no longer be cut called an atom. He said atoms are small hard particles. He thought atoms were made of single material with different shapes and sizes. -
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400BCE-Aristotle
Aristotle disagreed with Democritus ideas. He is also a Greek philosopher. He thought that you would never end up with a particle that could not be cut. He had a huge influence on people’s ideas that they soon thought he was right. -
1803 Dalton
He is a British chemist and school teacher that wanted to know why elements combine in certain proportions based on mass to form compounds. His research told him that elements combine in certain proportion because they are made of single atoms. -
1897 J. J. Thomson
Thomson- Also being a British scientist we found flaws with Dalton’s theory and did not agree with it. He discovered that there are small particles inside the atom. Which states that it can be divided into smaller parts. He used a cathode-ray tube. He showed that a positively charged plate attracted the beam. The beam consisted of negatively charged particles. He also concluded that every atom has negatively charged particles -
1909 Rutherford
He was a former student of Thomason’s named Ernest Rutherford and decided to question his old teacher’s theory. He aimed a beam of small positively charged particles at a thin sheet of gold foil. The coating glowed when hit by the positive particles. He had earlier put a light coating behind the foil so he could see where the particles hit. -
1911 Rutherford
In 1911 Rutherford revised the atomic theory while doing that he made a new model of the atom. He showed that in the center of the atom is a small extremely dense positively charged repel in the nucleus. If a particle were to head straight into the nucleus it would bounce back to its place and move around. He calculated that the nucleus was 100,000 times smaller than the dynamiter of a gold atom. -
1913- Niels Bohr
He was a Danish scientist who worked with Rutherford and studied the way atoms react to light. He proposed that electrons move around in a certain path or energy levels. In Bohr's model there is no path in one level but electrons can jump from path one level to a path in another. This was a valuable tool in predicting some atomic behavior but there was still room for improvement. -
20th century- Erwin Schrodinger and Werner Heisenburg
Erwin Schrodinger was an Austrian scientist along with his friend, Werner Heisenberg, which was a German physicist. They went into further explanations of the electrons in an atom. They said they the path of electrons have a path but you can never tell where the path is. According to the current theory there are regions inside the atom where are electrons are likely to be found. The regions are called electron clouds.
