the history of the atom

• Ernest Rutherford discovered that most of an atom's mass is concentrated in its center (the nucleus) and that it contains positively charged particles called protons.
• Niels Bohr proposed that electrons orbit around the nucleus at specific energy levels.
• Rutherford also found that electrons, which are negatively charged, orbit around the nucleus like planets orbiting the sun.
• jj Thompson created the plum pudding model and believed atoms were a cloud of positive charge with free floating negative elctrons
• John Dalton discoved the solid sphere model and said different spheres made up different elements
• Ernest Rutherford two students:

  gieger and marsden
• gold foil experiment:

  fired positively charged alpha particles at an extremely thin sheet of gold.

  expecting particles to pass straight through.

  1/8000 bounced back

  came up with nuclear model

  this said there was a tiny positive nucleus and an atom is mostly empty space
• bohr suggested that electrons only exist in a fixed orbit or shells and has a fixed energy.

  because rutherford model would collapse
• scientific theories

  more experiments new evidence found.

  new scientific knowledge new evidence which creates new ideas that can be used to make predictions.

  scientists also put their ideas for peer review and can check for errors and it help help develop their own work