An English chemist named John Dalton made many experiments, and from that evidence he inferred that atoms have certain characteristics. He made an atomic theory and model for the atom. Dalton thought that atoms were smooth, hard balls that could not be broken down. Dalton's model is compared to a pool ball.
Another English scientist, J.J. Thomson found atoms contain negatively charged particles. Thomson thought that there must be a positive charge. Thomson then made a model, and it described an atom with positive and negative charges scattered throughout the model. Later, the negatively charged particles became known as electrons. Thomson's model was compared to a muffin with berries or raisins.
One of Thomson's students, Ernest Rutherford, found evidence that countered Thomson's model. Rutherford's research team aimed a beam of positively charged particles of a thin sheet of gold foil. If Thomson's model was correct, then the beam would go through it in a straight line. Rutherford's model is compared to a seed of a peach.
A Danish scientist Niels Bohr revised the atomic model. He showed that electrons can only have only a specific amount of energy, leading to a certain orbit. His model was compared to an onion.
Scientist determined that electrons don't orbit the nucleus like planets. Electrons can be anywhere in a cloud-like region around the nucleus. The cloud is a visual model. It symbolizes where electrons are likely to be found.
English scientist James Chadwick discovered another particle in the nucleus of the atoms. The new particle was a neutron and it was hard to detect because it had no electric charge. Chadwick's discovery led to the change of the atomic model. Atom have a lot of empty space. At the center of an a tom is a tiny, massive nucleus containing protons and neutrons. Surrounding the nucleus is a cloud-like region of moving electrons.
