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1700-Dalton
A British chemist and school teacher wanted to know why elements combine in certain proportions based on mass to form compounds. -
1803-Dalton (Published)
In 1803 Dalton published his atomic theory that stated:- All substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed.
- Atoms of the same element are exactly alike, and atoms of different elements are different.
- Atoms join with other atoms to make new substances.
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1897-Thompson
A British scientist showed that there was a mistake in Dalton's theory. Atoms could be divided to smaller particles. He proved this with the cathode-ray tube. -
1909-Rutherford
A former student or Thompson's decided to test his theory by designing an experiment by aiming a bean at a thin sheet of gold foil. Rutherford put a specila coating behind the foil and the foil glowed when hit by the positively charged particles. Then you could see where the paticles went after they hit the gold foil. -
1911-Rutherford
Rutherford made a new model of the atom. He proposed that in the center of the atom there is a positively charged part that is called the nucleus. The nucleus is extremely dense and since like charges repel then he reasoned that positvely charged particles passed close by the nucleus. These were called electrons. -
1913-Bohr
A Danish scientist, Bohr was a scientist that worked with Rutherford. He studied the way that atoms react to light. He explained that electrons move around the nucleus in certain paths or energy levels. Bohr's model was a valuable tool in predicting some atomic behavior. -
1935-Schrodinger and Heisenberg
They explained the nature of electrons in the atom. They said that the exact path of an electron cannot be predicted. According to the current theory, there are regions inside the atom where electrons are likely to be found. These regions are called electron clouds. -
440 BC- Democritus
A Greek philoshopher that discovered the atom particle. The word atom means "not able to be divided." An atom is a small hard particle that could be one material formed into different shapes and sizes. -
368 BC-Aristotle
Was a Greek philoshopher who stated that by reasoning we can discover the essences of things. In his works on ethics and politics, he suggested that human happiness consists in living in conformity with nature.
