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500
Democritus
Around 500 B.C., Democritus made the first possible discovery of the atom. He reasoned that atoms were indivisible and indestructible. But couldn't build off of that because he had no experimental support and it was also not based on the scientific method. -
500
Democritus Model
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John Dalton
John Dalton made his first discovery relating to the atom in 1803. He studied the ratios of elements in chemical reactions and considered relative sizes and characters of atoms and how they fit together. Based on his experiments he created what is called Dalton's Atomic Theory. Dalton's Atomic Theory are theories and hypotheses based on his experiments. -
Dalton's Atomic Theory
The first one states that all elements are composed of tiny, invisible particles, also known as atoms. The second states that atoms of the same element are identical and atoms of diferent elements are different. Atoms of different elements can mix together physically and chemically to form compounds is the third one. The fourth and final hypothesis states that chemical reactions occur when atoms are seperated, joined or rearranged from eachother in different combinations. -
J.J. Thomson
J.J. Thomson perfomed experiments that involved passing an electric current through gases at a low pressure. During this experiment, he found that cathode rays are attracted to metal plates and would have a positive charge. He found that they can be deflected by a magnet. He later named cathode, electrons. He pictures electrons embed in a sphere of positice electrical charges. J.J. Thomson did discover the first electron. -
Bohr Model
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Rutherford Model
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Ernest Rutherford
Ernest Rutherford is known for discovering the nucleus of an atom. But in order to find that, he conducted an experiment called, Gold-Foil Experiment. In this experiment, he aimed a beam of alpha particles at a sheet of gold foil. He found out that most of the particles passed through and only some deflected. He concluded that they passed through because an atom is mostly empty space and mass is confined in the nucleus. And particles that approach the nucleus are greatly deflected. -
Niels Bohr
Niels Bohr discovered that the elctron moves in a circular orbit at fixed distances from the nucleus. He changed Ernest Rutherford's model to incorporate newer discoveries about how the energy of an atom changes when light is absorbed and released. He stated that electrons have a circular orbit and that each ring of the model can only hold a certain amount of particles. -
J.J. Thomson Model
J.J. Thomson's model shows that it is a sphere with a positive charge throughout bit has negatively charged particles (electrons).
