Sub-atomic particles

• Proton - positively charged, stable by itself, fairly heavy particle and

  resides in the dense nucleus.
• Neutron - no electric charge, also known as nucleons, located at the center of an atom.
• Electron - Negatively charged particles, much smaller than neutrons

  and protons, revolving somewhere

  outside the nucleus.
• Atomic number = Number of protons
• In a neutral element, number of proton = number of electron
• Mass number = Protons + Neutrons
• Neutrons = Mass number - protons