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440
Democritus Proposes the Atom
Democritus thought that there was a 'unbreakable particle' and called it a atom.
(440 B.C.) -
Dalton Creates an Atomic Theory Based on Experiments
1.) All substances are made of atoms, atoms are small particles that cannot be created, divided, or destroyed.
2.) Atoms of the same element are exactly alike and atoms of differnet elements are different.
3.) Atoms join with other atoms to form new substances. -
Thomson Finds Electrons in the Atom
Thomson discovered that there are small particles inside the atom, therefore atoms can be divivded into smaller parts.
Thomson repeated his experiment several times and found that the particle bean behaved in exactly the same way each time. He called the particles in the beam 'Corpuscles'.
Thomson revised the Atomic Theroy to account for the prescence of electrons. He realised that positive charges must be present to balance the negative charges of the electrons.
Model was called plum-pudding. -
The Modern Theory
Many twentieth-century scientists have contributed to our current understanding of the atom.
- An Austrian physicist named Erwin Schrödinger and a German physicist named Werner Heisenberg further explained the nature of electrons in the atom. They said that the electrons path cannot be determined. There are regions inside the atom where electrons are likely to be found- electron clouds. Electron clouds follow Bohr's model. -
Rutherford Opens an Atomic "Shooting Gallery"
Rutherford was a former student of Thomson's.
He designed an experiment where he aimed a beam of small, positivley charged particles at a thin sheet of gold foil to investigate the structure of an atom.The particles were smaller than protons.
Rutherford realized that the plum-pudding model did not exlain his results. He later revised the Atomic Theroy an devloped a new model of the atom to explain the deflectionof the particles. Rutherford proposed the nucleus as being tiny and extremely dense. -
Bohr States That Electrons Can Jump Between Levels
Niels Bohr was a Danish scientist that worked with Rutherford. He suggested that electrons travel around the nucleus in defintie paths. These paths are located in levels at certain distances from the nucleus. Bohr also proposed that no paths are located between the levels, but no electrons can jump from a path in one level to a path in another level. -
Aristotle Disagrees
Aristotle disagreed with Democritus and said that there would never be a invisible particle.
(384-322 B.C.)
