Thomson's Plum Pudding Model:
* Proposed: J.J. Thomson proposed this model in 1904.
* Description: It depicted the atom as a sphere of positively charged material with negatively charged electrons embedded throughout, like plums in a pudding.
* Assumptions: This model assumed that the atom's mass and positive charge were evenly distributed.
Rutherford's Gold Foil Experiment:
* Performed: Ernest Rutherford and his students, Hans Geiger and Ernest Marsden, conducted this experiment in 1911.
* Method: They bombarded a thin sheet of gold foil with alpha particles (positively charged particles).
* Expected Outcome: Based on Thomson's model, the alpha particles should have passed straight through the foil with minimal deflection, as the positive charge was assumed to be evenly distributed.
* Actual Outcome: A surprising number of alpha particles were deflected at large angles, some even bounced back directly towards the source.
Rutherford's Findings & the Nuclear Model:
* The Atom is Mostly Empty Space: The fact that most alpha particles passed straight through the gold foil indicated that atoms are mostly empty space.
* A Dense, Positively Charged Nucleus: The large deflections and backward scattering of some alpha particles suggested that the positive charge of the atom was concentrated in a small, dense region called the nucleus.
* Electrons Orbit the Nucleus: Based on the observations, Rutherford proposed that the negatively charged electrons orbit this positively charged nucleus.
Key Changes to the Atomic Model:
* The Plum Pudding model was wrong. The positive charge is not evenly distributed throughout the atom; it's concentrated in a small, dense nucleus.
* The atom is mostly empty space. The electrons orbit the nucleus at a significant distance, making the atom mostly empty.
Rutherford's experiment revolutionized our understanding of atomic structure and paved the way for further discoveries in nuclear physics.
