In
chemistry, an
ionic compound is a
chemical compound in which
ions are held together in a lattice structure by
ionic bonds. 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 force between oppositely charged bodies. Ionic compounds have a high melting and boiling point, and they are hard and very brittle.
Ions can be single atoms, as the
sodium and
chloride in common table salt
sodium chloride, or more complex groups such as the
carbonate in
calcium carbonate. 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
magnets.)
Chemical compounds are never strictly ionic. Even the most
electronegative/
electropositive pairs such as
caesium fluoride exhibit a degree of covalency. Similarly,
covalent compounds often exhibit charge separations. See also
HSAB theory.
Physical properties
Most ionic compounds are formed from a metal combined with non-metal.
Ionic compounds contain oppositly charged ions arranged in regular three dimensional lattices. For Example: sodium chloride consists of sodium ions (Na) and chloride ions (Cl). Each ion is held in the crystal lattice by strong elecctrostatic attraction to the oppositly charged ions around it IONIC BONDING
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. While ionic
inorganic compounds are solids at room temperature and usually form crystals, organic
ionic liquids are of increasing interest.
A valence electron configuration of 8 electron is referred to as a stable octet. Most elements obtain a stable octet when they bond.
The ions produced by electron transfer attract each other by electrostatic attraction and this creats 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 liquids. They are usually appreciably soluble in other polar solvents such as
alcohols,
acetone and
dimethyl sulfoxide as well. Ionic compounds tend not to dissolve in
nonpolar solvents such as
diethyl ether 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.
Electricity Conductivity
Solid ionic compounds cannot conduct electricity because there are no mobile ions or electrons present in the lattice. When the ionic compunds are dissolved in a liquid or molten, they can conduct electricity with the mobile ions.
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 the
Stock system) with the
oxidation number written in parenthesis, 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)).
See also
References