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- A greek philosopher named Democritus came up with the nept o atom.
- Small, hard particles that could not be divided.
- Democritus said that all atoms are always moving.
- All substances are made of atoms. Atoms are small prticles 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
J.J. Thomson- found electrons
- Thomson experimented with a cathode-Ray Tube.
- Thomson called the negatively charged particles coupuscles.
- We now call these negatively charged particles electrons.
- Thomsons Plum Pudding Model.
- His plum Piddung model showed a possible structure of the atom with the negative charges.
- Rutherford discoerved athat the atom had a small, dense nucleus than contained positive charges.
- Gold foil expirement- aimed charged particles at a thin sheet of gold foil.
- Trying to see where the positive particles would go.
- A particle that actually hit the nucleus would be delfected almost straight back.
Rutherfofords Planetary Model
- The atom is mostly empty space through which electrons travel.
- The atom has a small, dense, poisively harged nucleus. (Most of the mass is in the nucleus).
- Electrons travel around the nucleus like planets around the sun.
- In 1913, Niels Bohr determined that electrons traveled around the nucleus in definite paths.
- He also discovered that electrons could jump from a path in one level to a pth in another level.
- Schrodinger and Heisenberg explained that electrons do not travel in definite paths.
- electron paths cannot be predicted.
- The current theory suggests that electrons are found in regions called electron clouds.