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Period: 400 BCE to
Timeline
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460
Democritus
Democritus's atom. He proposed matter is made of tiny indivisible indestructible particles called atoms. His Ideas were rejected because He didn't have necessary equipment to test is ideas. -
John Dalton
John Dalton discovered that elements are made of atoms. An atom of hydrogen and an atom of carbon are different. Compounds are made of two or more different kinds atoms. The ratio of atoms in HCI is 1:1. The name of John Dalton's theory was called Dalton's Atomic theory. -
J. J. Thompson
J. J. Thompson discovered The electron. He found out that the charge of an electron is negative. Cathode rays are made of electrons and the electrons that move from the negative end of the tube to the positive end is opposite charges attract. When Thompson discovered cathode rays while working with gas discharge tubes -
Neils Bohr
Bohr's model can be called the planetary model because It resembles the solar system with planets orbiting the sun. Atoms in the same atom differ by their location. His fourth energy level can hold 32 electrons. To go to a higher energy level an electron must absorb energy. For an electron to fall from the third energy leevel to the second energy level, It must release energy. -
