4.1.3 - The Development of the Model of the Atom Flashcards
What was the original theory about atoms? (500BC)
Democritus - Believed that all matter was made up of tiny spheres (atoms) that could not be broken up.
What did John Dalton believe? (1804)
Agreed with Democritus but believed that each element was made up of different types of atoms.
What particle did J.J. Thomson discover?
Electrons that could be removed from atoms.
What was the Plum Pudding Model?
J.J. Thomson - A model of the atom suggesting that atoms were spheres of positive charge with negative electrons embedded inside of them.
Why was the Plum Pudding Model introduced?
The discovery of electrons proved that atoms had an internal structure and could be broken up/divided.
What experiment proved the Plum Pudding Model to be wrong?
The Alpha Scattering Experiment
What happened in the Alpha Scattering Experiment? (1909)
An experiment taken out by Ernest Rutherford where positive alpha particles were fired at a thin sheet of gold.
What were the expected results of the Alpha Scattering Experiment following the Plum Pudding Model of the atom?
That most particles would pass straight through the gold foil or only be slightly deflected.
What were the results of the Alpha Scattering Experiment?
Most particles passed straight through, but some were deflected more than expected, and a few completely deflected back the way they came.
What was concluded from a few alpha particles being deflected back in the Alpha Scattering Experiment?
That the mass of an atom was concentrated in a nucleus at the centre of the atom and that this nucleus had a positive charge as it repelled the positive alpha particles.
What was concluded from nearly all of the alpha particles passing straight through the gold foil in the Alpha Scattering Experiment?
That most of the atom is empty space.
What new model of the atom did the results of the Alpha Scattering Experiment lead to?
The Nuclear Model
What was the original Nuclear Model of the atom?
A positively charged nucleus surrounded by a cloud of negative electrons.
What did Niels Bohr contribute to the Nuclear Model of the atom?
He discovered that electrons orbited the nucleus in energy levels at specific distances from the nucleus.
What did evidence from further experiments suggest about the nucleus?
That it was made up of a group of particles (protons) that all had the same positive charge.
