Cyanide is not a metal, though the question of its identity often arises because it is used in industrial and mining processes involving metals. Cyanide is correctly classified as a chemical compound, specifically a polyatomic anion ($\text{CN}^{-}$) when dissolved in water or part of an ionic salt. Understanding why it is not a metal requires examining the chemical characteristics of both cyanide and metallic elements.
Defining Cyanide’s Chemical Identity
Cyanide refers to the chemical group characterized by a single carbon atom triple-bonded to a single nitrogen atom, represented by the formula $\text{CN}$. When this group carries a negative charge, it is the cyanide ion ($\text{CN}^{-}$), a polyatomic anion. This structure means the cyanide unit is not a standalone element but a molecule composed of two non-metal atoms: carbon and nitrogen.
The triple bond between carbon and nitrogen gives the cyanide ion its specific chemical properties and high reactivity. The cyanide ion is isoelectronic with carbon monoxide and molecular nitrogen, meaning they share the same number of electrons, which contributes to its linear geometry. Chemically, the cyanide ion is often categorized as a pseudohalogen because its behavior and ability to form salts are similar to halogen elements like chlorine and bromine.
What Makes Something a Metal
Metals are defined by a specific set of physical and chemical properties that cyanide does not possess. Metallic elements, such as iron, gold, or copper, are typically found on the left side of the periodic table. They are characterized by high electrical and thermal conductivity, a lustrous appearance, and the properties of malleability and ductility.
The ability of metals to conduct electricity results from their atomic structure, where valence electrons are delocalized, forming a “sea” of electrons surrounding the positive metal ions. This electron mobility allows for the efficient transfer of charge and heat. Chemically, metals tend to lose electrons easily, forming positively charged ions (cations) in chemical reactions.
Common Forms and Contexts of Cyanide
The term “cyanide” usually refers to compounds that contain the $\text{CN}^{-}$ anion, rather than the ion itself. The two most common forms are gaseous hydrogen cyanide ($\text{HCN}$) and various cyanide salts. Hydrogen cyanide is a volatile liquid or gas formed when the cyanide ion bonds with a hydrogen atom.
Cyanide salts are crystalline white solids, such as sodium cyanide ($\text{NaCN}$) and potassium cyanide ($\text{KCN}$). These compounds form when the non-metallic cyanide anion bonds ionically with a metal cation, like sodium ($\text{Na}^{+}$) or potassium ($\text{K}^{+}$). These salts are widely used in industrial processes, most notably for extracting gold and silver from ore in a process called cyanidation.