Wonderful! One of Dalton's main hypotheses was that the atom was the most fundamental particle. It could not be split into anything else. But, scientists observed that this was not true.
Scientists were able to discover subatomic particles because the subatomic particles had electric charge. You must have heard of positive and negative charges before. It is important to remember that if you have 2 positive or 2 negative charges, they repel each other (that is, they push each other apart). If you have one positive and one negative charge, the two charges attract each other.