Ten years later, Ernest Rutherford discovered that atoms have a very dense nucleus, which contains protons. In 1932, James Chadwick discovered the neutron, another particle located within the nucleus. And so scientists thought they had found the smallest atomic building blocks. This changed in 1963 when Murray Gell-Mann proposed his quark theory. Physicists have learned a great deal over the past 100 years.
Neutrons have no charge.
Here's a chance for you to construct a carbon atom. You'll start with a hydrogen atom, which contains one proton and one electron. Just add protons, neutrons, and electrons. You'll never succeed if you don't. If you are having trouble accessing the Atom Builder activity, try the non-Javascript version .