An atom is the smallest complete particle of an element. The three primary particles found in an atom are protons, neutrons, and electrons . The center part of an atom, where most of the mass is found, is called the nucleus . The particles in the nucleus of an atom are the protons and neutrons . Protons have a positive charge .
Neutrons have no charge.
The particles orbiting around the outside of the nucleus of an atom are electrons. Electrons have a negative charge. The maximum number of electrons found in the first energy level outside the nucleus of an atom is two. The maximum number of electrons found in the second energy level outside the nucleus of an atom is eight. A charged atom or particle is called an ion.