Ionic crystal

An ionic crystal is a crystal

Crystal

A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is crystallography...

 consisting of ion

Ion

An ion is an atom or molecule where the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge...

s bound together by their electrostatic attraction. Examples of such crystals are the alkali halides, including potassium fluoride

Potassium fluoride

Potassium fluoride is the chemical compound with the formula KF. After hydrogen fluoride, KF is the primary source of the fluoride ion for applications in manufacturing and in chemistry. It is an alkali metal halide and occurs naturally as the rare mineral carobbiite...

, potassium chloride

Potassium chloride

The chemical compound potassium chloride is a metal halide salt composed of potassium and chlorine. In its pure state it is odorless. It has a white or colorless vitreous crystal, with a crystal structure that cleaves easily in three directions. Potassium chloride crystals are face-centered cubic...

, potassium bromide

Potassium bromide

Potassium bromide is a salt, widely used as an anticonvulsant and a sedative in the late 19th and early 20th centuries. Its action is due to the bromide ion . Potassium bromide is presently used as a veterinary drug, as an antiepileptic medication for dogs and cats. It is a white crystalline...

, potassium iodide

Potassium iodide

Potassium iodide is an inorganic compound with formula KI. This white salt is the most commercially significant iodide compound, with approximately 37,000 tons produced in 1985. It is less hygroscopic than sodium iodide, making it easier to work with...

, sodium fluoride

Sodium fluoride

Sodium fluoride is the inorganic compound with the formula NaF. This colorless solid is a source of the fluoride ion in diverse applications. Sodium fluoride is less expensive and less hygroscopic than the related salt potassium fluoride....

, and other combinations of sodium

Sodium

Sodium is a metallic element with a symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals within "group 1"...

, caesium

Caesium

Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of , which makes it one of only five metals that are liquid at or near room temperature...

, rubidium

Rubidium

Rubidium is a chemical element with the symbol Rb and atomic number 37. Rb is a soft, silvery-white metallic element of the alkali metal group....

, or lithium

Lithium

Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number three. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...

 ions with fluoride

Fluorine

Fluorine is the chemical element with atomic number 9, represented by the symbol F. Fluorine forms a single bond with itself in elemental form, resulting in the diatomic F₂ molecule. F₂ is a supremely reactive, poisonous, pale, yellowish brown gas. Elemental fluorine is the...

, bromide

Bromine

Bromine , is a chemical element with the symbol Br and atomic number 35. A halogen element, bromine is a reddish-brown volatile liquid at standard room temperature that is intermediate in reactivity between chlorine and iodine. Bromine vapors are corrosive and toxic. Approximately 556,000 metric...

, chloride

Chlorine

Chlorine Chlorine Chlorine ( , from the Greek word 'χλωρóς' (khlôros, meaning 'pale green'), is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17 (formerly VII, VIIa, or VIIb). As the chloride ion, which is part of common salt and...

 or iodide

Iodine

Iodine , is a chemical element that has the symbol I and atomic number 53. Naturally-occurring iodine is a single isotope with 74 neutrons....

 ions.
NaCl has a 6:6 co-ordination.
The properties of NaCl reflect the strong interactions that exist between the ions. It is a good conductor of electricity when molten, but very poor in the solid state. When fused the mobile ions carry charge through the liquid.
They are characterized by strong absorption of infrared radiation and have planes along which they cleave easily.
The exact arrangement of ions in an ionic lattice varies according to the size of the ions in the solid.