ELECTRONIC TIMELINE

20TH CENTURY/ MODERN THEORY

• Electron paths cannot be predicted.
• Electrons are found in electron clouds,not paths.

1913/BOHR

• Electrons travel in definite paths.
• Electrons jump between levels from path to path.

1911/RUTHEFORD

• He conducted the gold foil experiment.
• There is a small, dense,positively charged nucleus.
• Most of an atom's mass is in the nucleus.
• Atoms contain mostly empty space.
• Electrons move in empty space in the atom.

1897/THOMSON

• He conducted the cathode-ray tube experiment.
• His theory of atomic structure led to the "plum-pudding" model.
• There are small, negatively charged particles inside an atom.

1803/DALTON

• Atoms of the same element are exactly alike.
• Atoms of different elements are different.
• Elements combine in specific proportions.
• He conducted experiments in combining elements.

440 B.C./ DEMOCRITUS

• Atoms are "uncuttable."
• Atoms are small,hard particles.
• Atoms constantly move.
• All substances are made of atoms.