The nucleus of an atom always has a positive net charge of one or greater. The presence of protons contained exclusively in the nucleus causes a positive charge.
All atoms contain at least one proton in their nuclei. Negatively charged electrons orbit an atom's nucleus, giving the atom a net charge of zero. Electrons move between atoms, creating compounds and causing chemical reactions; however, protons never move from their nuclei. Therefore, atoms with the same net charge in their nuclei are atoms of the same element. For example, a hydrogen atom contains one proton, producing a net charge of one in its nucleus.