A sulfide ion has a fixed charge of 2-. It is one of the common anions formed by the chemical element sulfur.
The smallest fundamental unit of an element that still retains all its properties is called an atom. A molecule, meanwhile, is the basic form of a chemical compound. When neutral atoms or molecules either lose or gain electrons, they become charged and are referred to as ions. Positively-charged particles are called "cations," while negatively-charged particles are known as "anions".
Ions are classified as either monoatomic ions, or those comprising only a single type of atom, or polyatomic ions, or those consisting of two or more types of atom. Oppositely-charged particles are likely to combine and form a "salt," which is the neutral product of a cation and an anion. The attractive force that holds these atoms or molecules together is in the form of ionic bonds.
Sulfur exists in nature in its elemental form, which is a yellowish, non-metallic, flammable crystalline powder. The element forms five anions, including two disulfide ions that are similar to peroxide ions and superoxide ions, two polysulfide ions and a sulfide ion. Aqueous solutions containing the sulfide ion are generally basic. When the sulfide ion is hydrolyzed, it produces hydrogen sulfide, which is characterized by a foul smell that is similar to rotten eggs.