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What Are Ionic Compounds?

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  • Written By: Ray Hawk
  • Edited By: E. E. Hubbard
  • Last Modified Date: 04 November 2016
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Ionic compounds are chemical compounds that are bound together by electrical charges of individually-charged ion atoms. Typically, an ionic compound is composed of positively-charged metals and negatively-charged nonmetals, and they form crystalline structures. Ordinary salt — NaCl — is one of the most common ionic compounds found in nature, consisting in basic form of a bond between a positively-charged sodium metal atom and a negatively-charged chlorine atom.

Properties of ionic compounds include their formation into lattice structures of crystals and their very high boiling and melting points. Their brittleness also gives them the tendency to fracture into equally-sized smaller crystals if struck with enough force. Crystalline ionic salts are also water soluble, and, once dissolved in water or in a pure liquid, molten state, are good conductors of electricity.

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Naming ionic compounds has always followed the tradition of using first the cation, or positively-charged ion, and tacking the name of the negatively-charged anion onto it. This is why salt is known as sodium chloride, with other examples being potassium iodide, silver nitrate, and mercury chloride. The total number of positive cation atoms and negative anion atoms is not included in the naming structure, as any ionic compound balances out these charges. A compound such as silver nitrate with the chemical formula of AgNO3 doesn't require a plural for the nitrate group. However, ionic elements like iron that can have a positive charge of two or three are commonly referred to with reference to this charge, such as Fe+2 being called iron (II).

In their natural form, ionic compounds are never strictly ionic or neutral in charge, and often have some degree of covalency — the sharing of electrons between different atomic energy shells. Electronegativity affects how strong the negative charge is in ionic compounds, with the Pauling scale rating fluorine as the most electronegative element at a rating of 4.0. Other elements, such as cesium, are the least electronegative at a level of 0.7. This varying level of electronegativity is used to help define covalent vs. ionic bonds. No electronegativity difference between bound atoms represents a pure, non-polar covalent bond, whereas a large electronegativity difference represents an ionic bond.

Metals in nature are found in the form of ionic compounds. This is because metals are largely reactive with carbon and oxygen in the presence of water, as well as elements like sulfur, phosphorus, and silicon. Therefore, the purification of metals generally starts with the mining of ionic compounds, such as sulphides, phosphates, carbonates, and most commonly oxides to produce pure elemental metals that can be used in industry.

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