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460
Democritus
Developed the idea of atoms. He asked this question: "If you break a piece of matter in half, and then break it in half again, how many breaks will you have to make before you can break it no further?" He called these basic matter particles, atoms. -
John Dalton
He performed experiments with various chemicals that showed matter. He recorded that it seemed to consist of lumpy particles -
Period: to
The History
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J.J. Thomson
He discovered the electron and proposed a model for the structure of the atom. The model was said to look like a raisins stuck on the surface of a lump of pudding. -
Max Planck
Max showed that when you vibrate atoms strong enough, you can measure the energy only in discrete units. He called these energy packets, quanta. -
Albert Einstein
Albert wrote a ground-breaking paper that explained that light absorption can release electrons from atoms, a phenomenon called the "photoelectric effect." -
Niels Bohr
Niels came up with two rules. RULE 1: Electrons can orbit only at certain allowed distances from the nucleus. RULE 2: Atoms radiate energy when an electron jumps from a higher-energy orbit to a lower-energy orbit. Also, an atom absorbs energy when an electron gets boosted from a low-energy orbit to a high-energy orbit. -
Ernest Rutherford
He finally identify the particles of the nucleus as discrete positive charges of matter.