Ionic compound

Ionic compound

Overview

In chemistry
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

, an ionic compound is a chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 in which ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

s are held together in a lattice structure by ionic bond
Ionic bond
An ionic bond is a type of chemical bond formed through an electrostatic attraction between two oppositely charged ions. Ionic bonds are formed between a cation, which is usually a metal, and an anion, which is usually a nonmetal. Pure ionic bonding cannot exist: all ionic compounds have some...

s. Usually, the positively charged portion consists of metal cations and the negatively charged portion is an anion or polyatomic ion. Ions in ionic compounds are held together by the electrostatic forces between oppositely charged bodies. Ionic compounds have high melting and boiling points, and they are hard and very brittle.

Ions can be single atoms, as the sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 and chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

 in common table salt sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...

, or more complex groups such as the carbonate
Carbonate
In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....

 in calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...

.
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In chemistry
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

, an ionic compound is a chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 in which ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

s are held together in a lattice structure by ionic bond
Ionic bond
An ionic bond is a type of chemical bond formed through an electrostatic attraction between two oppositely charged ions. Ionic bonds are formed between a cation, which is usually a metal, and an anion, which is usually a nonmetal. Pure ionic bonding cannot exist: all ionic compounds have some...

s. Usually, the positively charged portion consists of metal cations and the negatively charged portion is an anion or polyatomic ion. Ions in ionic compounds are held together by the electrostatic forces between oppositely charged bodies. Ionic compounds have high melting and boiling points, and they are hard and very brittle.

Ions can be single atoms, as the sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 and chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

 in common table salt sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...

, or more complex groups such as the carbonate
Carbonate
In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, . The name may also mean an ester of carbonic acid, an organic compound containing the carbonate group C2....

 in calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...

. But to be considered an ion, they must carry a positive or negative charge. Thus, in an ionic bond, one 'bonder' must have a positive charge and the other a negative one. By sticking to each other, they resolve, or partially resolve, their separate charge imbalances. Positive to positive and negative to negative ionic bonds do not occur. (For an easily visible analogy, experiment with a pair of bar magnet
Magnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...

s.)

Chemical compounds are never strictly ionic. Even the most electronegative/electropositive pairs such as caesium fluoride
Caesium fluoride
Caesium fluoride , is an inorganic compound usually encountered as a hygroscopic white solid. It is more soluble and more readily dissociated than sodium fluoride or potassium fluoride. It is available in anhydrous form, and if water has been absorbed it is easy to dry by heating at 100 °C for...

 exhibit a degree of covalency. Similarly, covalent compounds
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....

 often exhibit charge separations. See also HSAB theory
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

.

Physical properties

Physical Properties Ionic Compounds
States (at room temperature) Solid
Electrical conductivity Solid: No   Liquid: Yes   Aqueous: Yes (if soluble)
Boiling point and Melting Point High
Solubility in water Often high
Thermal conductivity Low

Characteristics


Ionic compounds have strong electrostatic bonds between particles. As a result, they generally have very high melting and boiling points. They also have good electrical conductivity when molten or in aqueous solution
Aqueous solution
An aqueous solution is a solution in which the solvent is water. It is usually shown in chemical equations by appending aq to the relevant formula, such as NaCl. The word aqueous means pertaining to, related to, similar to, or dissolved in water...

. While ionic inorganic compound
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

s are solids at room temperature and usually form crystals, organic ionic liquid
Ionic liquid
An ionic liquid is a salt in the liquid state. In some contexts, the term has been restricted to salts whose melting point is below some arbitrary temperature, such as . While ordinary liquids such as water and gasoline are predominantly made of electrically neutral molecules, ILs are largely made...

s are of increasing interest.

The ions produced by electron transfer attract each other by electrostatic attraction and this creates an ionic bond.

Solubility


Following the aphorism, "like dissolves like", ionic compounds dissolve in polar solvents, especially those that ionize, such as water and ionic liquid
Ionic liquid
An ionic liquid is a salt in the liquid state. In some contexts, the term has been restricted to salts whose melting point is below some arbitrary temperature, such as . While ordinary liquids such as water and gasoline are predominantly made of electrically neutral molecules, ILs are largely made...

s. They are usually appreciably soluble in other polar solvents such as alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

s, acetone
Acetone
Acetone is the organic compound with the formula 2CO, a colorless, mobile, flammable liquid, the simplest example of the ketones.Acetone is miscible with water and serves as an important solvent in its own right, typically as the solvent of choice for cleaning purposes in the laboratory...

 and dimethyl sulfoxide
Dimethyl sulfoxide
Dimethyl sulfoxide is an organosulfur compound with the formula 2SO. This colorless liquid is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is miscible in a wide range of organic solvents as well as water...

 as well. Ionic compounds tend not to dissolve in nonpolar solvents such as diethyl ether
Diethyl ether
Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula . It is a colorless, highly volatile flammable liquid with a characteristic odor...

 or petrol.

When the oppositely charged ions in the solid ionic lattice are surrounded by the opposite pole of a polar molecule, the solid ions are pulled out of the lattice and into the liquid. When this force is more than the electrostatic attraction of the lattice, the ions become dissolved in the liquid.

Electrical conductivity


Solid ionic compounds cannot conduct electricity because there are no mobile ions or electrons present in the lattice. When the ionic compounds are dissolved in a liquid or molten, they can conduct electricity with the mobile ions that allowed the electricity passed through it.

Name


According to the IUPAC, an ionic compound's common name is written using two words. The name of the cation comes first (when using stock nomenclature
Stock nomenclature
Stock nomenclature for inorganic compounds is a widely used system of chemical nomenclature developed by the German chemist Alfred Stock and first published in 1919...

 with the oxidation number
Oxidation number
In coordination chemistry, the oxidation number of a central atom in a coordination compound is the charge that it would have if all the ligands were removed along with the electron pairs that were shared with the central atom. Oxidation numbers are often confused with oxidation states.The...

written in parentheses, followed by the name of the anion. For example, Fe2(SO4)3 is named as iron(III) sulfate. If the Classical naming system is being used, some ionic compounds have special "old" names, such as ferric (iron(III)), ferrous (iron(II)), cupric (copper(II)), and cuprous (copper(I)).