Atom
An atom is made of three main particles: the proton, the neutron, and the electron. Protons and neutrons have nearly the same size and mass (about  grams). The mass of an electron is about 1800 times smaller (about  grams).  Protons have a positive charge, electrons have a negative charge, and neutrons have no charge. Most atoms have no charge. The number of protons (positive) and electrons (negative) are the same, so the charges balance out to zero. However, ions have a different number of electrons than protons, so they have a positive or negative charge.