Atoms are unstable and decay through alpha, beta, or gamma emissions, forming new elements. Alpha particles have a +2 charge and knock out electrons, while beta particles have a -1 charge and are faster. Gamma rays are electromagnetic waves that penetrate deeply. Radioactive decay is used in carbon dating, medical tracers, sterilization, and more. Radiation can ionize atoms and damage DNA, potentially causing cancer, so precautions like shielding and limiting exposure time are important.