Antimatter
Other antimatter particles are the same way, where they have the same weight, and look and act the same as regular particles, but their electrical charge is the opposite of regular particles. Antihydrogen, for example, has the positron, which is positively charged, orbiting around an antiproton, which is negatively charged, which is the opposite way regular hydrogen looks, which has the electron (negative charge), orbiting around a proton (positive charge).