An atom is a neutral particle that does not carry any charge on it. This is because the protons (positive) and electrons (negative) are equal in number and balance the charge out. Now when an atom gains or loses electrons, the number is no longer the same. Therefore, the atom now gains a charge. If an electron is lost, there is one extra positive charge on the ion (because one proton is not being balanced against). If an electron is gained a negative ion is formed because now there are more electrons than protons. Positively charged ions are known as cations and negatively charged ions are known as anions.