An atom that carries an electrical charge is known as an ion. This charge arises when a neutral atom gains or loses electrons. When an atom gains one or more electrons, it develops a net negative charge and is called an anion. The chemical symbol S2- represents a sulfur atom that has acquired two extra electrons. The superscript “2-” indicates this specific charge, meaning there are two more electrons than protons.
The Base Element: Sulfur
The neutral atom at the core of this anion is sulfur, a nonmetal element found in Group 16 of the periodic table. In its neutral state, sulfur has an atomic number of 16, and its outermost valence shell contains six electrons.
Atoms strive for chemical stability, often achieved by having a full outer electron shell, known as the octet rule. For sulfur, a full shell requires eight valence electrons. Since the neutral sulfur atom already has six, it tends to gain exactly two electrons to complete its octet. This gain of two negative charges results in the ion’s charge of -2, forming the stable S2- anion.
Naming Conventions for Negative Ions
The process of naming single-atom anions, or monoatomic anions, follows a standardized system. The rule dictates taking the root of the element’s name, removing the original ending, and attaching the suffix “-ide.” This communicates that the species is a single, negatively charged atom.
Following this convention, the name of the S2- ion is the sulfide ion. The element name “sulfur” is truncated to “sulf-” and the “-ide” suffix is added. This rule applies uniformly across the periodic table for simple anions.
For example, a chlorine atom (Cl) gains one electron to become Cl-, named the chloride ion. Similarly, an oxygen atom (O) gains two electrons to form the O2- ion, known as the oxide ion.
Where Sulfide Ions Are Found
The sulfide ion appears in various forms throughout the natural world.
Environmental Presence
One of its most recognizable compounds is hydrogen sulfide (H2S), a noxious gas known for its rotten-egg smell. This gas is often produced in anaerobic environments, such as swamps and sewers, where sulfate-reducing bacteria convert sulfate into sulfide.
Biological Role
In biological systems, the sulfide ion is an essential component of life, primarily incorporated into amino acids. Two protein-building amino acids, cysteine and methionine, contain sulfur atoms, making the element a necessary nutrient. Sulfide compounds also function as signaling molecules within the body, influencing physiological processes.
Geological Importance
Geologically, sulfide compounds form a large class of minerals known as sulfide minerals. Many economically significant metal ores are sulfides, where the metal is chemically bonded to the sulfide ion. Examples include galena (lead sulfide), sphalerite (zinc sulfide), and pyrite, or “fool’s gold,” which is an iron sulfide compound.