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Ionic bond
 
 
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An ionic bond is a type of chemical bond
Chemical bond

A chemical bond is the physical process responsible for the attractive interactions between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds....
 that involves a metal
Metal

In chemistry, a metal is a chemical element whose atoms readily lose electrons to form positive ions , and form metallic bonds between other metal atoms and ionic bonds between nonmetal atoms....
 and a non-metal ion
Ion

An ion is an atom or molecule which has lost or gained one or more electrons, giving it a positive or negative electrical charge. According to the Bohr_model this will be from or in the outer shield 'n'....
s (or polyatomic ions such as ammonium
Ammonium

The ammonium cation is a positively electric charge polyatomic ion of the chemical formula NH4+. It has a formula weight of 18.05 and is formed by protonation of ammonia ....
) through electrostatic attraction. In short, it is a bond formed by the attraction between two oppositely charged ions.

The metal donates one or more electron
Electron

The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....
s, forming a positively charged ion or cation with a stable electron configuration
Electron configuration

In atomic physics and quantum chemistry, electron configuration is the arrangement of electrons in an atom, molecule, or other physical structure....
. These electrons then enter the non metal, causing it to form a negatively charged ion or anion which also has a stable electron configuration.






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Encyclopedia


An ionic bond is a type of chemical bond
Chemical bond

A chemical bond is the physical process responsible for the attractive interactions between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds....
 that involves a metal
Metal

In chemistry, a metal is a chemical element whose atoms readily lose electrons to form positive ions , and form metallic bonds between other metal atoms and ionic bonds between nonmetal atoms....
 and a non-metal ion
Ion

An ion is an atom or molecule which has lost or gained one or more electrons, giving it a positive or negative electrical charge. According to the Bohr_model this will be from or in the outer shield 'n'....
s (or polyatomic ions such as ammonium
Ammonium

The ammonium cation is a positively electric charge polyatomic ion of the chemical formula NH4+. It has a formula weight of 18.05 and is formed by protonation of ammonia ....
) through electrostatic attraction. In short, it is a bond formed by the attraction between two oppositely charged ions.

The metal donates one or more electron
Electron

The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....
s, forming a positively charged ion or cation with a stable electron configuration
Electron configuration

In atomic physics and quantum chemistry, electron configuration is the arrangement of electrons in an atom, molecule, or other physical structure....
. These electrons then enter the non metal, causing it to form a negatively charged ion or anion which also has a stable electron configuration. The electrostatic attraction between the oppositely charged ions causes them to come together and form a bond.

For example, common table salt is sodium chloride
Sodium chloride

Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the chemical formula SodiumChlorine....
. When sodium (Na) and chlorine (Cl) are combined, the sodium
Sodium

Sodium is an element which has the symbol Na , atomic number 11, atomic mass 23 amu , and a common oxidation number +1. Sodium is a soft, silvery white, highly reactive element and is a member of the alkali metals within "group 1" ....
 atoms each lose an electron, forming a cation (Na+), and the chlorine
Chlorine

Chlorine...
 atoms each gain an electron to form an anion (Cl-). These ions are then attracted to each other in a 1:1 ratio to form sodium chloride (NaCl).
Na + Cl ? Na+ + Cl- ? NaCl


Ionic Bonding
The removal of electrons from the atoms is endothermic and causes the ions to have a higher energy. There may also be energy changes associated with breaking of existing bonds or the addition of more than one electron to form anions. However, the attraction of the ions to each other lowers their energy. Ionic bonding will occur only if the overall energy change for the reaction is favourable – when the bonded atoms have a lower energy than the free ones. The larger the resulting energy change the stronger the bond. The low electronegativity
Electronegativity

Electronegativity, symbol χ, is a chemical property that describes the ability of an atom to attract electrons towards itself in a covalent bond....
 of metals and high electronegativity of non-metals means that the energy change of the reaction is most favorable when metals lose electrons and non-metals gain electrons. An ionic bond doesn't need metal.

Pure ionic bonding is not known to exist. All ionic compounds have a degree of covalent bond
Covalent bond

A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or between atoms and other covalent bonds....
ing. The larger the difference in electronegativity
Electronegativity

Electronegativity, symbol χ, is a chemical property that describes the ability of an atom to attract electrons towards itself in a covalent bond....
 between two atoms, the more ionic the bond. Ionic compounds conduct electricity
Electricity

Electricity is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena such as lightning and static electricity, but in addition, less familiar concepts such as the electromagnetic field and electromagnetic induction....
 when molten or in solution. They generally have a high melting point
Melting point

The melting point of a solid is the temperature range at which it changes states of matter from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium....
 and tend to be soluble in water.

Ionic structure

Ionic compound
Ionic compound

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....
s in the solid state form lattice structures, The two principal factors in determining the form of the lattice are the relative charges of the ions and their relative sizes. Some structures are adopted by a number of compounds, for example the rock salt, sodium chloride
Sodium chloride

Sodium chloride, also known as common salt, table salt, or halite, is a chemical compound with the chemical formula SodiumChlorine....
, structure is adopted by many alkaline earth halides and binary oxides such as MgO
Magnesium oxide

Magnesium oxide, or magnesia, is a white solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of ....
.

Strength of an ionic bond


For a solid crystalline ionic compound the enthalpy change in forming the solid from gaseous ions is termed the lattice energy
Lattice energy

The lattice energy of an Ionic bond solid is a measure of the strength of bonds in that ionic compound. It is usually defined as the enthalpy of formation of the ionic compound from gaseous ions and as such is invariably exothermic....
. The experimental value for the lattice energy
Lattice energy

The lattice energy of an Ionic bond solid is a measure of the strength of bonds in that ionic compound. It is usually defined as the enthalpy of formation of the ionic compound from gaseous ions and as such is invariably exothermic....
 can be determined using the Born-Haber cycle
Born-Haber cycle

The Born-Haber cycle is an approach to analyzing reaction energy. It was named after and developed by the two Germans scientists Max Born and Fritz Haber....
. It can also be calculated using the Born-Landé equation
Born-Landé equation

The Born-Land? equation is a means of calculating the lattice energy of a crystalline ionic compound. In 1918 Max Born and Alfred Land? proposed that the lattice energy could be derived from the electrostatic potential of the ionic lattice and a repulsive potential energy term....
 as the sum of the electrostatic potential energy, calculated by summing interactions between cations and anions, and a short range repulsive potential energy term. The electrostatic potential can be expressed in terms of the inter-ionic separation and a constant (Madelung constant
Madelung constant

The Madelung constant is used in determining the energy of a single ion in a crystal. It is named after Erwin Madelung, a German physicist.Because the anions and cations in an Ionic compound are attracted to each other by virtue of their opposing charges, separating the ions requires a certain amount of energy....
) that takes account of the geometry of the crystal. The Born-Landé equation
Born-Landé equation

The Born-Land? equation is a means of calculating the lattice energy of a crystalline ionic compound. In 1918 Max Born and Alfred Land? proposed that the lattice energy could be derived from the electrostatic potential of the ionic lattice and a repulsive potential energy term....
 gives a reasonable fit to the lattice energy of e.g. sodium chloride where the calculated value is -756 kJ/mol which compares to -787 kJ/mol using the Born-Haber cycle
Born-Haber cycle

The Born-Haber cycle is an approach to analyzing reaction energy. It was named after and developed by the two Germans scientists Max Born and Fritz Haber....
.

Polarization effects

Ion
Ion

An ion is an atom or molecule which has lost or gained one or more electrons, giving it a positive or negative electrical charge. According to the Bohr_model this will be from or in the outer shield 'n'....
s in crystal lattices of purely ionic compounds are spherical
Sphere

A sphere is a symmetrical geometrical object. In non-mathematical usage, the term is used to refer either to a round ball or to its two-dimensional surface....
; however, if the positive ion is small and/or highly charged, it will distort the electron cloud of the negative ion, an effect summarised in Fajans' rules
Fajans' rules

In inorganic chemistry, Fajans' Rules, formulated by Kasimir Fajans in 1923, are used to predict whether a chemical bond will be covalent bond or ionic bond, and depend on the charge on the cation and the relative sizes of the cation and anion....
. This polarization of the negative ion leads to a build-up of extra charge density between the two nuclei
Atomic nucleus

The nucleus of an atom is the very dense region, consisting of nucleons , at the center of an atom. Although the size of the nucleus varies considerably according to the mass of the atom, the size of the entire atom is comparatively constant....
, i.e., to partial covalency. Larger negative ions are more easily polarized, but the effect is usually only important when positive ions with charges of 3+ (e.g., Al3+) are involved. However, 2+ ions (Be2+) or even 1+ (Li+) show some polarizing power because their sizes are so small (e.g., LiI is ionic but has some covalent bonding present). Note that this is not the ionic polarization
Ionic polarization

In chemistry, ionic polarization is polarization which is caused by relative displacements between positive and negative ions in ionic crystals ....
 effect which refers to displacement of ions in the lattice due to the application of an electric field.

Ionic versus covalent bonds

In an ionic bond, the atoms are bound by attraction of opposite ions, whereas, in a covalent bond
Covalent bond

A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or between atoms and other covalent bonds....
, atoms are bound by sharing electrons. In covalent bonding, the molecular geometry
Molecular geometry

Molecular geometry or molecular structure is the three-dimensional arrangement of the atoms that constitute a molecule. It determines several properties of a substance including its Reactivity , Chemical polarity, Phase , color, magnetism, and biological activity....
 around each atom is determined by VSEPR rules, whereas, in ionic materials, the geometry follows maximum packing
Close-packing

In geometry, close-packing of spheres is the construction of an infinite regular arrangement of identical spheres so that they take up the greatest possible fraction of an infinite 3-dimensional space ....
 rules.

Electrical conductivity

Ionic substances in solution conduct electricity because the ions are free to move and carry the electrical charge from the anode to the cathode.
Ionic substances conduct electricity when molten for the same reason i.e. that ions are free to move.
Some ionic compounds conduct electricity when solid, this is due to migration of ions under the influence of an electric field. (see Fast ion conductor
Fast ion conductor

Fast ion conductors, also known as solid electrolytes and superionic conductors, are solid electrical conductors which conduct due to the movement of ions through voids in their crystal lattice....
)

Substances in ionic form

Common Cations
Stock System NameFormulaHistoric Name
Simple Cations
AluminiumAl3+ 
BariumBa2+ 
BerylliumBe2+ 
CaesiumCs+ 
CalciumCa2+ 
Chromium(II)Cr2+Chromous
Chromium(III)Cr3+Chromic
Chromium(VI)Cr6+Chromyl
Cobalt(II)Co2+Cobaltous
Cobalt(III)Co3+Cobaltic
Copper(I)Cu+Cuprous
Copper(II)Cu2+Cupric
Copper(III)Cu3+ 
Gallium Ga3+ 
Gold(I)Au+ 
Gold(III)Au3+ 
Iron(II)Fe2+Ferrous
Iron(III)Fe3+Ferric
Lead(II)Pb2+Plumbous
Lead(IV)Pb4+Plumbic
LithiumLi+ 
MagnesiumMg2+ 
Manganese(II)Mn2+Manganous
Manganese(III)Mn3+Manganic
Manganese(IV)Mn4+ 
Manganese(VII)Mn7+ 
Mercury(II)Hg2+Mercuric
Nickel(II)Ni2+Nickelous
Nickel(III)Ni3+Nickelic
PotassiumK+ 
SilverAg+ 
SodiumNa+ 
StrontiumSr2+ 
Tin(II)Sn2+Stannous
Tin(IV)Sn4+Stannic
ZincZn2+ 
Polyatomic Cations
AmmoniumNH4+ 
HydroniumH3O+ 
NitroniumNO2+ 
Mercury(I)Hg22+Mercurous
Common Anions
Formal NameFormulaAlt. Name
Simple Anions
ArsenideAs3- 
AzideN3- 
BromideBr- 
ChlorideCl- 
FluorideF- 
HydrideH- 
IodideI- 
NitrideN3- 
OxideO2- 
PhosphideP3- 
SulfideS2- 
PeroxideO22- 
Oxoanions
ArsenateAsO43- 
ArseniteAsO33- 
BorateBO33- 
BromateBrO3- 
HypobromiteBrO- 
CarbonateCO32- 
Hydrogen carbonateHCO3-Bicarbonate
ChlorateClO3- 
PerchlorateClO4- 
ChloriteClO2- 
HypochloriteClO- 
ChromateCrO42- 
DichromateCr2O72- 
IodateIO3- 
NitrateNO3- 
NitriteNO2- 
PhosphatePO43- 
Hydrogen phosphateHPO42- 
Dihydrogen phosphateH2PO4- 
PermanganateMnO4- 
PhosphitePO33- 
SulfateSO42- 
ThiosulfateS2O32- 
Hydrogen sulfateHSO4-Bisulfate
SulfiteSO32- 
Hydrogen sulfiteHSO3-Bisulfite
Anions from Organic Acids
AcetateC2H3O2- 
FormateHCO2- 
OxalateC2O42- 
Hydrogen oxalateHC2O4-Bioxalate
Other Anions
Hydrogen sulfideHS-Bisulfide
TellurideTe2- 
AmideNH2- 
CyanateOCN- 
ThiocyanateSCN- 
CyanideCN-


See also

  • Coulomb's law
    Coulomb's law

    Coulomb's law, sometimes called the Coulomb law, is an equation describing the electrostatic force between electric charges. It was developed in the 1780s by French physicist Charles Augustin de Coulomb and was essential to the development of the classical electromagnetism....
  • Linear combination of atomic orbitals
  • Hybridization
  • Chemical polarity
    Chemical polarity

    In chemistry, polarity refers to the dipole-dipole intermolecular forces between the slightly electric charge end of one molecule to the negative end of another or the same molecule....


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