Chemistry -- Subatomic Particles
The exploration of atomic structure began in 1911, when Ernest Rutherford, a New Zealander who worked in Canada and England, discovered that atoms had a dense central nucleus that contained positively charged particles, which he named protons.
Except for the simplest hydrogen atom with a single proton as its entire nucleus, all atoms contain neutrons (particles that are electrically neutral) in addition to protons. For most of the light elements, the numbers of protons and neutrons in the nucleus are nearly equal. The sum of protons and neutrons is the mass number of an atom.
Ready to combine all of these particles into your own atom? Explore the Atom Builder from PBS. (This exercise requires the Shockwave plug-in.)