MODELS OF THE ATOM Flashcards
Thomsons model
States that atoms are negatively-charged particles are imbedded in positively-charged sphere, like plums in a plum pudding
Daltons model
atoms are like a smooth, solid sphere that cannot be broken down into smaller pieces.
Components of the Gold foil experiment
A piece of gold foil was hit with alpha particles, which have a positive charge. Most alpha particles went right through. This showed that the gold atoms were mostly empty space. Most of the mass of an atom is located in the centre of the atom.
What were the 3 main findings of the gold foil experiement
Atoms consists mostly of empty space, the nucleus is small and dense, the nucleus has a positive charge
Observation : Most alpha particles travel through the foil undetected
Finding : the Atom is mostly empty space
Observation : Some alpha particles are deflected by small angles
Finding : The nucleus is positively charged, as is the alpha particle
Observation : Occasionally, an alpha particle deflects back from the foil
Finding : The nucleus carries most of the atoms mass
Why was Rutherfords experiment held in a vacuum
To ensure that the alpha particles did not collide with the air particles, as if the alpha particles collided with the air particles then the former would scatter. making the conclusions of the experiment invalid
Why did Rutherford not expect alpha particles to be deflected by the gold
As the plum pudding model was still believed to be accurate, meaning the positive charge of the atom was evenly distributed throughout. As a consequence the positively charged alpha particles would not experience strong electrostatic forces and would not be deviated a great distance / angle
Most alpha particles passed through the gold foil with little or no deflection
This suggested that most of the atom is empty space, since the alpha particles, which are relatively heavy and positively charged, passed through without being slowed down or deflected significantly.
Some alpha particles were deflected at small angles
a small number of alpha particles being deflected at large angles suggested that there is a concentration of positive charge in the atom - like charges repel, so the positive alpha particles were being repelled by positive charges
Some Alpha Particles Were Reflected Directly Back
the very small number of alpha particles coming straight back suggested that the positive charge and mass are concentrated in a tiny volume in the atom (the nucleus)
