Rutherford preformed an experiment using positively charged particles fired at gold foil. Through his experience, he proved that atoms are not a "pudding" filled with positively charge material. He theorized that atoms have small dense, positively charged center, which he called the nucleus. he said nucleus is tiny compared to the atom as a whole, because the atom is mostly open space. his conclusion was that the negatively charged particles are scattered outside the nucleus at a distance.