The addition and subtraction of negatively charged electrons can easily change an atom’s charge, because they perpetually spin in valence shells outside the nucleus. It is easier for a neighboring atom to share or steal an electron rather than a positively charged proton, which is found in the nucleus. It requires a strong energy input to split a proton free from other protons and neutrons. thus, the atoms lose or gain electrons from neighboring ones and become what is known as "ions". Hope it helped!