Short answers, pulled from the story.
J. J. Thomson proposed his atomic model in 1905, imagining electrons floating inside a sphere of uniform positive charge. He described this positive electricity as a liquid with cohesion to keep it from flying apart under its own repulsion.
In 1909 Ernest Marsden observed that approximately one in eight thousand alpha particles bounced back from the gold foil. This result contradicted Thomson's model which predicted such an event would be undetectable.
The team favored gold due to its extreme malleability which allowed them to create extremely thin foils. They tested various metals but selected gold because its properties enabled the necessary experimental conditions.
Rutherford later described his shock at these results during a lecture delivered on the 15th of October 1936 at Cambridge University. He stated that the probability of deflection exceeding ninety degrees should have been zero according to existing theories.
Rutherford estimated the central charge qn to be about plus one hundred units based on this data. The derivation proved that single collisions could produce large deflections if the target was sufficiently dense.