Formation of Ions

An ion is an atom or a group of atoms which is/are electrically charged. They are electrically charged by losing or gaining one or more electrons. This happens for the outermost shell to be fully charged and also makes it stable. An atom with equal number of protons and electrons is known as neutral.

When neutral atoms lose electrons, they become positively charged and are called cations. Examples of cations: Na+ (Sodium ion), K+ (Potassium ion).

When neutral atoms gain electrons, they become negatively charged and are called anions. Examples of anions: Cl- (Chloride), O2- (Oxide).

Some elements do not combine with other elements. This is because they have fully filled outermost shell. This makes them stable or unreactive. Examples of such elements from the first twenty elements are Helium, Neon and Argon.