what is ion

An ion is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convention. Ions can be formed by the addition or removal of electrons from neutral atoms or molecules, or by the combination of ions with other particles. Ions can be positively charged, called cations, or negatively charged, called anions. Ions consisting of only a single atom are termed atomic or monatomic ions, while two or more atoms form molecular ions or polyatomic ions. Many crystalline substances are composed of ions held in regular geometric patterns by the attraction of the oppositely charged particles for each other. Ions can be created using radiation such as x-rays, and ionizing radiation is often used to diagnose or treat a medical condition.