Plum Pudding Model

Thomson's work led to the proposal of the plum pudding model.
The plum pudding dessert was popular at the time, consisting of raisins baked in a bread-like custard.

Description of the Model:
- An atom is envisioned as a mass of positively charged material.
- Electrons float within this positive mass, similar to how raisins float in plum pudding or chocolate chips in cookies.
Comparison to Earlier Models:
- This model contrasts with Dalton's model, which depicted the atom as a solid, indivisible sphere.
Charge Neutrality:
- The positive charge balances the negative charge from the electrons, keeping the atom neutral.

Robert Milliken conducted groundbreaking research on the charge of the electron.
Experiment Setup:
- Milliken sprayed oil droplets into an electric field, where the droplets became charged as they entered.
- By adjusting the electric field, he could suspend a charged droplet in midair while others fell.
Calculating Charge:
- He compared the gravitational force acting on the droplet with the electric force to determine the charge of the electron.
Results of the Experiment:
- The charge measured consistently at 1.6 x 10^(-19) coulombs.
Thomson’s Contribution:
- Thomson provided a ratio of mass to charge of an electron, finding that for every 1 gram of electrons, there is 1.76 x 10^(8) coulombs of charge.
Mass Calculation:
- Using the charge and Thomson's ratio, Milliken calculated the mass of an electron to be approximately 9.10 x 10^(-28) grams.

While the plum pudding model explained Thomson's results, it was not the final word.
Rutherford's Experiment:
- Scientist Ernest Rutherford sought to test the validity of the plum pudding model.
- His experiment involved firing positively charged particles at a thin layer of gold foil with a detector to observe deflections.