How did Dalton prove that atoms exist?
He noticed the amounts of gases reacted in various whole number ratios.
Therefore must be different building blocks with definite and characteristic weights.
How does Dalton’s model describe atoms?
Small indestructible spheres called atoms and stated:
All matter is made of atoms.
Atoms of the same element have the same average mass, size and unique properties.
Atoms cannot be converted into atoms of another element through chemical reactions.
Atoms of different elements combine in specific proportions to form compounds.
How did Thompson prove that electrons exist and that they are negative?
Experimented with cathode ray tubes which create beams of small particles. He placed charged plates on either side of the beam to determine its charge.
Observed that the beams are deflected towards positively charged plates. The beam must contain negative particles because opposite charges attract.
Since atoms are neutral, they must contain negative particles that can be removed from a positive material.
Describe Thompson’s model
Atoms are positively charged spheres with embedded negative electrons (Plum Pudding Model).
How did Rutherford prove the nucleus exists and that it is positive?
Shot positively charged alpha particles from radioactive elements at a thin piece of gold foil.
Observed that most particles went straight through. Some deflected at large angles back towards the particle gun.
Since most alpha particles went straight through, atoms are made of mainly empty space. The ones that deflected back must have hit a dense positive structure because they were repelled off.
