Describe the most up-to-date model of the atom before the alpha particle experiment.

Hello,
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Before Rutherford proposed his
model of the atom, the most up to date model of the atom was the one proposed by by J. J.
Thomson in 1904, the so-called "Plum pudding model".

At the time, Thomson knew that atoms were made up of negatively charged electrons. But
since atoms were also known to have a neutral electric charge, Thomson had to assume that the
atom also had "something" in it with a positive charge to balance out the negative
charge from the electrons.

With this in mind, Thomson thought of three models
that would best fit this description:

1. Each electron would have a
   positive charge as a pair;
2. The electrons would orbit a central region of
   net positive charge;
3. The electrons would occupy a region of
   net positive charge, as if there was a "soup" with positive charge in this
   region.

Thomson decided to go with the third
option for his model, where the pudding in the name came from.

The model lost
its place to the one proposed by Ernest Rutherford in 1911his student at the time. He conducted
an experiment where he shot alpha particles (helium nuclei) into a sheet of gold and observed
the trajectories of these particles. The data lead him into discarding his professor's model, as
it didn't describe the data as well as it should.

Rutherford's model was
similar to the second option first proposed by Thomson. In this model, the atom was made up of a
central positively charged particle (the nucleus), which would have electrons in its
orbit.