radioactive. Super-heavy atoms are stable this is likely unbiheksium, with 184 protons 126 neutrons.
Each particle of matter have antimatter particles each with the opposite electric charges. Thus, antielektron positron is positively charged, protons and antiprotons are negatively charged, when matter and antimatter meet, they annihilate each other. There is an imbalance between the number of particles of matter and antimatter. Imbalance is still not completely understood, although there are theories that explain bariogenesis possible. Antimatter is not found naturally.
However, in 1996, successfully synthesized in antihidrogen CERN laboratory in Geneva. There is also a rare atoms other one made by replacing protons, neutrons, or electrons with other particles are equally charged.
For example, electrons can be replaced with a heavier muon, muon atomic form. Types of atoms can be used to test the predictions of physics.
